System and process for removal of pollutants from a gas stream

ABSTRACT

System for removal of targeted pollutants, such as oxides of sulfur, oxides of nitrogen, mercury compounds and ash, from combustion and other industrial process gases and processes utilizing the system. Oxides of manganese are utilized as the primary sorbent in the system for removal or capture of pollutants. The oxides of manganese are introduced from feeders into reaction zones of the system where they are contacted with a gas from which pollutants are to be removed. With respect to pollutant removal, the sorbent may interact with a pollutant as a catalyst, reactant, adsorbent or absorbent. Removal may occur in single-stage, dual-stage, or multi-stage systems with a variety of different configurations and reaction zones, e.g., bag house, cyclones, fluidized beds, and the like. Process parameters, particularly system differential pressure, are controlled by electronic controls to maintain minimal system differential pressure, and to monitor and adjust pollutant removal efficiencies. Reacted sorbent may be removed from the reaction action zones for recycling or recycled or regenerated with useful and marketable by-products being recovered during regeneration.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.09/919,600 filed on Jul. 31, 2001, now U.S. Pat. No. 6,610,263 whichclaims priority to the following U.S. Provisional Applications: No.60/222,236, filed Aug. 1, 2000; Nos. 60/232,049; 60/232,097, both filedSep. 12, 2000; No. 60/238,105, filed Oct. 4, 2000; Nos. 60/239,422;60/239,435, both filed Oct. 10, 2000; No. 60/242,830, filed Oct. 23,2000; No. 60/243,090, filed Oct. 24, 2000; No. 60/244,948, filed Nov. 1,2000; Nos. 60/288,166; 60/288,165; 60/288,237; 60/288,245; 60/288,243;60/288,242; 60/288,168; 60/288,167, all filed May 2, 2001; Nos.60/295,930; 60/296,006; 60/296,005; 60/296,004; 60/296,007; 60/296,003;all filed Jun. 5, 2001; and Nos. 60/299,362; 60/299,363, both filed Jun.19, 2001, all of which are incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to the systems and processes for removal ofpollutants, such as oxides of sulfur, oxides of nitrogen, fly ash,mercury compounds, and elemental mercury from gases generated from theburning of fossil fuels and other process gases with electronic controlof operational parameters such as, differential pressure across thesystem, gas temperature, and removal efficiency. The systems andprocesses of the invention employ oxides of manganese as the primarysorbent to effect removal of pollutants, such as oxides of sulfur and/oroxides of nitrogen, and may further employ other sorbent materials andchemical additives separately and in conjunction with oxides ofmanganese to effect the removal of other target pollutants, e.g., usingalumina to remove mercury.

BACKGROUND OF THE INVENTION

During combustion of fuels that contain sulfur compounds, oxides ofsulfur (SO_(X)), such as sulfur dioxide (SO₂), and sulfur trioxide (SO₃)are produced as a result of oxidation of the sulfur. Some fuels maycontain nitrogen compounds that contribute to the formation of oxides ofnitrogen (NO_(X)), which are primarily formed at high temperatures bythe reaction of nitrogen and oxygen from the air used for the reactionwith the fuel. These reaction compounds, SO_(X) and NO_(X), are reportedto form acids that may contribute to “acid rain.” Federal and stateregulations dictate the amount of these and other pollutants, which maybe emitted. The regulations are becoming more stringent and plantoperators are facing greater difficulties in meeting the regulatoryrequirements. Many technologies have been developed for reduction ofSO_(X) and NO_(X), but few can remove both types of pollutantssimultaneously in a dry process or reliably achieve cost effectivelevels of reduction.

In the past to meet the regulatory requirements, coal-burning powerplants have often employed a scrubbing process, which commonly usescalcium compounds to react with SO_(X) to form gypsum. This wasteproduct is normally discarded as a voluminous liquid slurry in animpoundment and ultimately is capped with a clay barrier, which is thencovered with topsoil once the slurry is de-watered over time.Alternatively, some power-plant operators have chosen to burn coal thatcontains much lower amounts of sulfur to reduce the quantities of SO_(X)emitted to the atmosphere. In the case of NO_(X), operators often chooseto decrease the temperature at which the coal is burned. This in turndecreases the amount of NO_(X) produced and therefore emitted; however,low temperature combustion does not utilize the full heating value ofthe coal, resulting in loss of efficiency.

Turbine plants normally use natural gas, which contains little or nosulfur compounds, to power the turbines, and therefore virtually noSO_(X) is emitted. On the other hand at the temperature that theturbines are commonly operated, substantial NO_(X) is produced. Inaddition to Selective Catalytic Reduction (SCR) processes for conversionof NO_(X) to nitrogen, water vapor, and oxygen, which can be safelydischarged, some operators choose to reduce the temperature at which theturbines are operated and thereby reduce the amount of NO_(X) emitted.With lower temperatures the full combustion/heating value of natural gasis not realized, resulting in loss of efficiency. Unfortunately forthese operators, newer environmental regulation will require evengreater reduction of SO_(X) and NO_(X) emissions necessitating newer ormore effective removal technologies and/or further reductions inefficiency.

Operators of older coal-burning power plants are often running out ofspace to dispose of solid wastes associated with use of scrubbers thatuse calcium compounds to form gypsum. Operators of newer plants wouldchoose to eliminate the problem from the outset if the technology wereavailable. Additionally, all power plants, new and old, are faced withupcoming technology requirements of further reducing emissions of NO_(X)and will have to address this issue in the near future. Thus, plantsthat currently meet the requirements for SO_(X) emissions are facingstricter requirements for reduction of NO_(X) for which there has beenlittle or no economically feasible technology available.

The nitrogen oxides, which are pollutants, are nitric oxide (NO) andnitrogen dioxide (NO₂) or its dimer (N₂O₄). The relatively inert nitricoxide is often only removed with great difficulty relative to NO₂. Thelower oxide of nitrogen, nitrous oxide (N₂O), is not considered apollutant at the levels usually found in ambient air, or as usuallydischarged from air emission sources. Nitric oxide (NO) does however;oxidize in the atmosphere to produce nitrogen dioxide (NO₂). The sulfuroxides considered being pollutants are sulfur dioxide (SO₂) and sulfurtrioxide (SO₃).

Typical sources of nitrogen and sulfur oxide pollutants are power plantstack gases, automobile exhaust gases, heating-plant stack gases, andemissions from various industrial process, such as smelting operationsand nitric and sulfuric acid plants. Power plant emissions represent anespecially formidable source of nitrogen oxides and sulfur oxides, byvirtue of the very large tonnage of these pollutants and such emissionsdischarged into the atmosphere annually. Moreover, because of the lowconcentration of the pollutants in such emissions, typically 500 ppm orless for nitrogen oxides and 3,000 ppm or less for sulfur dioxide, theirremoval is difficult because very large volumes of gas must be treated.

Of the few practical systems, which have hitherto been proposed for theremoval of nitrogen oxides from power plant flue gases, all have certaindisadvantages. Various methods have been proposed for the removal ofsulfur dioxide from power plant flue gases, but they too havedisadvantages. For example, wet scrubbing systems based on aqueousalkaline materials, such as solutions of sodium carbonate or sodiumsulfite, or slurries of magnesia, lime or limestone, usually necessitatecooling the flue gas to about 55° C. in order to establish a waterphase. At these temperatures, the treated gas requires reheating inorder to develop enough buoyancy to obtain an adequate plume rise fromthe stack. U.S. Pat. No. 4,369,167 teaches removing pollutant gases andtrace metals with a lime slurry. A wet scrubbing method using alimestone solution is described in U.S. Pat. No. 5,199,263.

Considerable work has also been done in an attempt to reduce NO_(X)pollutants by the addition of combustion catalysts, usuallyorgano-metallic compounds, to the fuel during combustion. However, theresults of such attempts have been less successful than stagedcombustion. NO_(X) oxidation to N₂ is facilitated by ammonia, methane,et al. which is not effected by SO_(X) is described in U.S. Pat. No.4,112,053. U.S. Pat. No. 4,500,281 teaches the limitations oforgano-metallic catalysts for NO_(X) removal versus staged combustion.Heavy metal sulfide with ammonia is described for reducing NO_(X) instack gases in U.S. Pat. No. 3,981,971.

Many fuels, and particularly those normally solid fuels such as coal,lignite, etc., also contain substantial amounts of bound or fuel sulfurwith the result that conventional combustion produces substantialamounts of SO_(X) pollutants which are also subject to pollutioncontrol. It has generally been the opinion of workers in the art thatthose conditions employed in staged combustion, particularly two-stagerich-lean combustion for NO_(X) reduction, will likewise lower the levelof SO_(X) emissions. However, it has been found that little or noreduction in SO_(X) emissions can be obtained in a two-stage, rich-leancombustion process. Indeed, it has been found that the presence ofsubstantial amounts of sulfur in a fuel also has a detrimental effect onNO_(X) reduction in a two-stage, rich-lean process.

Considerable effort has been expended to remove sulfur from normallysolid fuels, such as coal, lignite, etc. Such processes include wetscrubbing of stack gases from coal-fired burners. However, such systemsare capital intensive and the disposal of wet sulfite sludge, which isproduced as a result of such scrubbing techniques, is also a problem.Cost inefficiencies result from the often-large differential pressuresacross a wet scrubber removal system; differential pressures in excessof 30 inches of water column (WC) are not unusual. Also, the flue gasesmust be reheated after scrubbing in order to send them up the stack,thus reducing the efficiency of the system. Both U.S. Pat. Nos.4,102,982 and 5,366,710 describe the wet scrubbing of SO_(X) and NO_(X).

In accordance with other techniques, sulfur scavengers are utilized,usually in fluidized bed burners, to act as scavengers for the sulfurand convert the same to solid compounds which are removed with the ash.The usual scavengers in this type of operation include limestone(calcium carbonate) and dolomite (magnesium-calcium carbonate) becauseof availability and cost. However, the burning techniques are complexand expensive to operate and control; and the burner equipment iscomparatively expensive. Dissolving coal or like material in a moltensalt compound is described in U.S. Pat. No. 4,033,113. U.S. Pat. No.4,843,980 teaches using alkali metal salt during the combustion of coalor other carbonaceous material with further efficiency by adding a metaloxide. A sulfur scavenger added upstream to a combustion zone isdescribed in U.S. Pat. No. 4,500,281.

The combustion gas stream from a coal-burning power plant is also amajor source of airborne acid gases, fly ash, mercury compounds, andelemental mercury in vapor form. Coal contains various sulfides,including mercury sulfide. Mercury sulfide reacts to form elementalmercury and SO_(X) in the combustion boiler. At the same time othersulfides are oxidized to SO_(X) and the nitrogen in the combustion airis oxidized to NO_(X). Downstream of the boiler, in the ducts and stackof the combustion system, and then in the atmosphere, part of theelemental mercury is re-oxidized, primarily to mercuric chloride(HgCl₂). This occurs by reactions with chloride ions or the likenormally present in combustion reaction gases flowing through thecombustion system of a coal-burning power plant.

Many power plants emit daily amounts of up to a pound of mercury, aselemental mercury and mercury compounds. The concentration of mercury inthe stream of combustion gas is about 4.7 parts per billion (ppb) or0.0047 parts per million (ppm). Past efforts to remove mercury from thestream of combustion gas, before it leaves the stack of a power plant,include: (a) injection, into the combustion gas stream, of activatedcarbon particles or particulate sodium sulfide or activated aluminawithout sulfur; and (b) flowing the combustion gas stream through a bedof activated particles. When activated carbon particle injection isemployed, the mercuric chloride in the gas stream is removed from thegas stream in a bag house and collected as part of a powder containingother pollutants in particulate form. Mercuric chloride and otherparticulate mercury compounds that may be in the gas stream can be morereadily removed from the gas stream at a bag house than can elementalmercury. Activated carbon injection for mercury removal along with anactivated particle bed is described in U.S. Pat. No. 5,672,323.

When the gas stream flows through a bed of activated carbon particles,mercury compounds are adsorbed on the surface of the activated carbonparticles and remain there. Elemental mercury, usually present in vaporform in combustion gases, is not adsorbed on the activated carbon to anysubstantial extent without first being oxidized into a compound ofmercury. U.S. Pat. No. 5,607,496 teaches the oxidation of mercury andsubsequent absorption to particles and utilization of alumina aredescribed therein.

Sodium sulfide particle injection can be utilized to form mercuricsulfide (HgS), which is more readily removable from the gas stream at abag house than is elemental mercury. The conversion of mercury to asulfide compound with subsequent capture in a dust separator is detailedin U.S. Pat. No. 6,214,304.

Essentially, all of the above techniques create solid waste disposalproblems. The solids or particulates, including fly ash, collected atthe bag house and the spent activated carbon removed from the bed ofactivated carbon, all contain mercury compounds and thus pose specialproblems with respect to burial at landfills where strictly localizedcontainment of the mercury compounds is imperative. The concentration ofmercury compounds in particulates or solids collected from a bag houseis relatively minute; therefore, a very small quantity of mercury wouldbe dispersed throughout relatively massive volumes of a landfill,wherever the bag house solids or particulates are dumped. Moreover, withrespect to activated carbon, that material is relatively expensive, andonce spent activated carbon particles are removed from an adsorbent bed,they cannot be easily regenerated and used again.

In the activated alumina process, mercury compounds in the gas streamcan be adsorbed and retained on the surface of activated particles, butmuch of the elemental mercury will not be so affected. Thus elementalmercury in the combustion gas stream is oxidized to form mercurycompounds (e.g. mercuric chloride), and catalysts are employed topromote the oxidation process. However, such processes do not captureSO_(X) and NO_(X).

The use of oxides of manganese to remove sulfur compounds from gasstreams is known in the art. Oxides of manganese are known to formsulfates of manganese from SO_(X) and nitrates of manganese from NO_(X)when contacted with a gas containing these pollutants. U.S. Pat. No.1,851,312 describes an early use of oxides of manganese to remove sulfurcompounds from a combustible gas stream. U.S. Pat. No. 3,150,923describes a dry bed of oxides of manganese to remove SO_(X). A wetmethod to remove SO_(X) with oxides of manganese is described in U.S.Pat. No. 2,984,545. A special filter impregnated with manganese oxide toremove totally reduced sulfur compounds is described in U.S. Pat. No.5,112,796. Another method in U.S. Pat. No. 4,164,545 describes using anion exchange resin to trap the products of manganese oxide and SO_(X)and NO_(X). The use of certain types of oxides of manganese to removeSO_(X) is disclosed U.S. Pat. Nos. 3,723,598 and 3,898,320. Some of theknown methods of bringing oxides of manganese in contact with a gasstream, i.e., sprayed slurries, beds of manganese ore or specialfilters, have been cumbersome. Although the prior art teaches the use ofoxides of manganese to remove SO_(X) and/or NO_(X), they do not teach anadaptable system or process that can capture SO_(X) and/or NO_(X) andother pollutants with oxides of manganese and monitor and adjust systemoperational parameters, such as differential pressure, to providereal-time system control.

Bag houses have traditionally been used as filters to removeparticulates from high volume gas streams. U.S. Pat. No. 4,954,324describes a bag house used as a collector of products generated throughthe use of ammonia and sodium bicarbonate to remove SO_(X) and NO_(X)from a gas stream. U.S. Pat. No. 4,925,633 describes a bag house as asite of reaction for SO_(X) and NO_(X) with the reagents, ammonia andalkali. U.S. Pat. No. 4,581,219 describes a bag house as a reactor forhighly efficient removal of SO_(X) only with a calcium-based reagent andalkaline metal salt. Although these prior art discloses and teach theuse of bag houses for removal of particulates and as a reaction chamber,they do not teach the use of bag houses in an adaptable system capableof monitoring and adjusting system operational parameters, such asdifferential pressure, to capture SO_(X) and/or NO_(X) and otherpollutants with oxides of manganese.

In view of the aforementioned problems of known processes for removal ofSO_(X), NO_(X), mercury compounds, and elemental mercury as well asother pollutants from combustion gases, process gases, and otherindustrial waste gases, it would be desirable to provide a dry processfor removal of SO_(X) and NO_(X) as well as other pollutants from a gasstream. It is further desirable to have a dry removal process thateliminates the environmental impacts of the disposal of large volumes ofmercury containing solids and particulates and significant amounts ofgypsum generated during SO_(X) wet removal processes.

Wet removal processes can result in significant differential pressuresacross a removal system. Differential pressures above 30 inches of watercolumn have been observed in wet removal processes. Such largedifferential pressures are costly because significant energy must beexpended to counter the differential pressure and provide a waste gasstream with sufficient energy to flow up and out of a stack. A systemand process that can accomplish pollutant removal with minimal orcontrolled differential pressure across the system therefore would bedesirable and cost effective for most industry sectors processing oremitting significant amounts of combustion gases, process gases, andother industrial gases.

The calcium compounds utilized in SO_(X) wet scrubbing methods formgypsum in the process. They are purchased and consumed in significantquantities and once gypsum is formed the calcium compounds cannot berecovered, at least not cost-effectively. Thus, it would be desirable tohave a removal method employing a sorbent that not only can removepollutants from a gas stream but that can be regenerated, recovered, andthen recycled or reused for removal of additional pollutants from a gasstream.

To realize such a system and process, it would need to incorporateprocess controls and software that can monitor and adjust operationalparameters from computer stations onsite or at remote locations throughinterface with a sophisticated electronics network incorporating anindustrial processor. This would allow a technician to monitor andadjust operational parameters in real-time providing controls of suchoperational parameters as system differential pressure and pollutantcapture rates or removal efficiencies. Such a network would be desirablefor its real-time control and off-site accessibility.

In light of increased energy demand and recent energy shortages, itwould be desirable to be able to return to operational utility idledpower plants that have been decommissioned because their gypsumimpoundments have reached capacity. This could be accomplished withretrofits of a system employing a regenerable sorbent in a dry removalprocess that does not require the use of calcium compounds. Such asystem would also be readily adapted and incorporated into new powerplants that may be coming on line. Utility plants and independent powerplants currently in operation could readily be retrofitted with such asystem. Further, such a system could be of significant value in enablingemissions sources to comply with emission standards or air qualitypermit conditions. With the reductions in emissions of pollutants suchas NO_(X) and SO_(X), marketable emissions trading credits could be madeavailable or non-attainment areas for state or national ambient airquality standards may be able to achieve attainment status. Suchscenarios would allow for development in areas where regulatoryrequirements previously prohibited industrial development or expansion.

The systems and processes of the present invention in their variousembodiments can achieve and realize the aforementioned advantages,objectives, and desirable benefits.

SUMMARY OF THE INVENTION

The invention is directed to an adaptable system for dry removal ofSO_(X) and/or NO_(X) and/or other pollutants from gases and to processesemploying the system. The system generally comprises a feeder and atleast one reaction zone for single-stage removal. For dual-stage removalthe system would generally be comprised of one or more feeders, a firstreaction zone, and a second reaction zone. Multi-stage removal systemswould incorporate additional reaction zones. The reaction zones utilizedin the invention may be a fluidized bed, a pseudo-fluidized bed, areaction column, a fixed bed, a pipe/duct reactor, a moving bed, a baghouse, an inverted bag house, bag house reactor, serpentine reactor, anda cyclone/multiclone. Process operational parameters, such as systemdifferential pressure, can be monitored and adjusted so that anydifferential pressure across the system is no greater than apredetermined level. Such process controls are accomplished with controlsub-elements, control loops and/or process controllers.

The feeder contains a supply of sorbent of regenerable oxides ofmanganese and/or regenerated oxides of manganese. The feeder isconfigured to handle and feed oxides of manganese, which, uponregeneration, are in particle form and are defined by the chemicalformula MnO_(X), where X is about 1.5 to 2.0 and wherein the oxides ofmanganese have a particle size of about 0.1 to about 500 microns andsurface area of about 1 to about 1000 m²/g as determined by theBrunauer, Emmett and Teller (BET) method.

For single stage removal of SO_(X) and/or NO_(X), a gas containingSO_(X) and/or NO_(X) is introduced into a reaction zone. The gas wouldbe introduced at temperatures typically ranging from ambient temperatureto below the thermal decomposition temperature(s) of nitrates ofmanganese if NO_(X) only or both NO_(X) and SO_(X) were to be removed.If only SO_(X) is the target pollutant, the gas would be introduced attemperatures typically ranging from ambient temperature to below thethermal decomposition temperature(s) of sulfates of manganese. In thereaction zone, the gas is contacted with the sorbent for a timesufficient to effect SO_(X) capture at a targeted SO_(X) capture rateset point or for a time sufficient to effect NO_(X) capture at a targetcapture rate set point. The SO_(X) and NO_(X), being capturedrespectively by reacting with the sorbent to form sulfates of manganeseto substantially strip the gas of SO_(X) and to form nitrates ofmanganese to substantially strip the gas of NO_(X). The reaction zone isconfigured to render the gas free of reacted and unreacted sorbent sothat the gas can be vented from the reaction zone.

In a two-stage removal system, the first reaction zone is configured forintroduction of the sorbent and a gas containing SO_(X) and NO_(X). Thegas is introduced at temperatures typically ranging from ambienttemperature to below the thermal decomposition temperature(s) ofsulfates of manganese and contacted with the sorbent for time sufficientto primarily effect SO_(X) capture at a targeted SO_(X) capture rate setpoint. The SO_(X) is captured by reacting with the sorbent to formsulfates of manganese to substantially strip the gas of SO_(X). Thesecond reaction zone is configured for introduction of sorbent and thegas that has been substantially stripped of SO_(X) from the firstreaction zone. In the second reaction zone, the gas is introduced attemperatures typically ranging from ambient temperature to below thethermal decomposition temperature(s) of nitrates of manganese and isfurther contacted with sorbent for a time sufficient to primarily effectNO_(X) capture at a targeted NO_(X) capture rate set point. The NO_(X)is captured by reacting with the sorbent to form nitrates of manganeseto substantially strip the gas of NO_(X). The second reaction zone isfurther configured so that the gas that has been substantially strippedof SO_(X) and NO_(X) is rendered free of reacted and unreacted sorbentso that the gas may be vented from the second reaction zone.

In another embodiment, the system further comprises control sub-elementsor combinations of control sub-elements for regulating and controllingdifferential pressure across the system, for regulating and controllingSO_(X) and/or NO_(X) capture efficiency, for regulating sorbent feedrate, for regulating gas inlet temperatures into the reaction zones, forregulating variable venturi position, and for simultaneous monitoring,regulation and control of differential pressure, SO_(X) and NO_(X)capture rates, sorbent feed rate, inlet temperatures and variableventuri position. The control sub-element for regulating and adjustingdifferential pressure does so by measuring differential pressure acrossthe system, comparing differential pressure measurements againstdifferential pressure set points, and increasing or decreasing pulserates to adjust differential pressure to reconcile with targeteddifferential pressure set points.

In another embodiment, the system is generally comprised of at least onesorbent feeder and a modular reaction unit. Said feeder contains asupply of sorbent of regenerable oxides of manganese and/or regeneratedoxides of manganese. The feeder is configured to handle and feed oxidesof manganese, which, upon regeneration, are in particle form and aredefined by the chemical formula MnO_(X) where X is about 1.5 to 2.0, andwherein the oxides of manganese have a particle size of less than 100microns and a surface area of at least 20 m²/g as determined by the BETmethod. The modular reaction unit is comprised of at least threeinterconnected reaction zones. With the reaction zones as bag houses,the bag houses are connected so that a gas containing SO_(X) and/orNO_(X) can be routed through any one of the bag houses, any two of thebag houses in series, or all of the at least three bag houses in seriesor in parallel or any combination of series and parallel. Each bag houseof the modular reaction unit is separately connected to the feeder sothat sorbent can be introduced into each bag house where SO_(X) and/orNO_(X) capture can occur and the gas is contacted with sorbent for atime sufficient to allow formation of sulfates of manganese, nitrates ofmanganese, or both. This embodiment may further comprise theabove-mentioned control sub-elements. Additionally, the modular reactionunit may further comprise a section of pipe/duct connected to an inletof each bag house for conveying gas to each bag house and into whichsorbent can be introduced. The section of pipe/duct may be configured asa first reaction zone where gas containing SO_(X) and NO_(X) isintroduced at temperatures typically ranging from ambient temperature tobelow the sorbent sulfate and nitrate thermal decompositiontemperature(s) thereof and contacted with the sorbent for a timesufficient to effect SO_(X) capture at a targeted SO_(X) capture rateset point, the SO_(X) being captured by reacting with the sorbent toform sulfates of manganese. The bag houses of the modular reaction unitsare each configured so that the gas substantially stripped of SO_(X) orNO_(X) is rendered free of reacted and unreacted sorbent so that the gasmay be vented.

In another embodiment of the invention, the system is comprised of atleast one feeder and multiple bag houses. The first bag house isconnected to the second and third bag houses through a common conduit.The first bag house is configured for introduction of sorbent and a gascontaining SO_(X) and NO_(X) where the gas is introduced at temperaturestypically ranging from ambient temperature to below the thermaldecomposition temperature(s) of sulfates of manganese and contacted withthe sorbent for a time sufficient to primarily effect SO_(X) capture ata SO_(X) capture rate set point, the SO_(X) being captured by reactingwith the sorbent to form sulfates of manganese to substantially stripthe gas of SO_(X). The first bag house is configured to render the gasthat has been substantially stripped of SO_(X) free of reacted andunreacted sorbent so that the gas can be directed out of the first baghouse free of reacted and unreacted sorbent. The second bag house andthe third bag house are each connected to the first bag house by acommon conduit. In the second bag house and the third bag house the gasthat has been substantially stripped of SO_(X) in the first bag housemay be introduced at temperatures typically ranging from ambient tobelow the thermal decomposition temperature(s) of nitrates of manganeseand is further contacted with sorbent for a time sufficient to primarilyeffect NO_(X) capture at a targeted NO_(X) capture rate set point. TheNO_(X) is captured by reacting with the sorbent to form nitrates ofmanganese to substantially strip the gas of NO_(X). The second and thirdbag houses each being configured to render the gas that has beensubstantially stripped of SO_(X) and NO_(X) free of reacted andunreacted sorbent so that the gas may be vented from the second andthird bag houses free of reacted and unreacted sorbent. The system ofthis embodiment also includes diverter valve(s) positioned in the commonconduit to direct the flow of gas from the first bag house to the secondbag house and/or the third bag house. The diverter valve(s) havevariable positions which may include first, second and third positions,and so on in sequence. In the one position, gas from the first bag houseis directed to the second bag house. In another position, gas from thefirst bag house is directed to both the second and third bag houses. Andin a further position, gas from the first bag house is directed to thethird bag house. Differential pressure within the system is regulated sothat any differential pressure across the system is no greater than apredetermined level.

In its various embodiments, the system may further comprise an aluminareactor where the gas that has been substantially stripped of SO_(X)and/or NO_(X) can be introduced and contacted with the sorbent for thepurpose of removing mercury. In the reactor, mercury compounds in thegas contacts the sorbent, which may be oxides of manganese and/oralumina, and is sorbed thereon. The reactor is configured to render thegas free of sorbent so that the gas can be vented.

In another embodiment of the invention, the bag house utilized asreaction zones in the system may be an inverted bag house. The invertedbag house permits downward, vertical flow of gases and sorbent and iscomprised of a bag house housing, at least one inlet, a plurality offabric filter bags, a support structure for the filter bags, a hopper toreceive and collect particles, an outlet, and a conduit. The bag househousing permits the introduction of gases and sorbent entrained in thegases, has a top and a bottom and is configured for gases to flowvertically downward from the top to the bottom of the bag house. Saidinlet is located near the top of the bag house housing and configuredfor the introduction of gases and sorbent entrained in the gases intothe bag house. The plurality of fabric filter bags are configured toallow gas to flow from the outside of the bags to the inside of the bagsunder an applied differential pressure and to prevent the passage ofsorbent from the outside to the inside of the bags, thereby separatingsorbent from the gas. The support structure is configured to receive andsupport the fabric filter bags and to provide openings through whichparticles may be freely passed downward into the hopper by gravity. Thehopper is configured to receive the particles and to permit the removalof the particles. The inverted bag house also has an outlet located nearthe bottom of the housing below the bags and above the hopper. Theoutlet is connected to a conduit located below the fabric filter bagsand positioned to receive gas passing through the fabric filter bags.

The invention is further directed to a bag house reactor that can beutilized as a reaction zone in the system of the invention. The baghouse reactor is comprised of a bag house that has interior and exteriorsurfaces as well as upper, central, and lower sections. The bag househas a variable venturi for adjusting the velocity of gas flowing withinthe bag house thereby increasing of decreasing the depth of thepseudo-fluidized bed. The variable venturi is generally located in thecentral and/or lower sections of the bag house and is configured foradjustment of the position of the variable venturi by varying thedistance or space between the variable venturi and the interior surfaceof the bag house. The bag house reactor has a variable venturi positiondetector for determining the position of the variable venturi and avariable venturi positioner for adjusting the position of the variableventuri to increase or decrease the velocity of gas flow from the lowersection past the variable venturi to the central and upper sections ofthe bag house. There is a first distribution port which is configuredfor introduction of gas into the bag house. The gas distribution port ispositioned below the variable venturi. There is a distribution portconnected to a sorbent feeder conduit which is configured forintroduction of sorbent into the bag house. The sorbent distributionport is positioned above the variable venturi. Within the bag house area plurality of fabric filter bags secured therein. The fabric filterbags are mounted in the upper section of the bag house and extenddownward into the central section. In the lower section of the bag houseis a sorbent hopper where loaded sorbent is collected. The bag housereactor has a loaded sorbent outlet connected to the sorbent hopper. Thesorbent outlet has an outlet valve which in the open position allows forremoval of sorbent from the hopper. Located in the top section of thebag house is a vent for the venting of gas from the bag house.

The invention is further directed to processes employing systemsaccording to the invention for removal of SO_(X) and NO_(X) from a gas.Thus in another embodiment of the invention, the process comprisesproviding a removal system according to the invention, introducing gascontaining SO_(X) and NO_(X) into the first reaction zone of the system,the gas having temperatures typically ranging from ambient temperatureto below the thermal decomposition temperature(s) of sulfates ofmanganese; contacting the gas with sorbent for a time sufficient toprimarily effect SO_(X) capture at a targeted SO_(X) capture rate setpoint by formation of sulfates of manganese; passing the gassubstantially stripped of SO_(X) from the first reaction zone into thesecond reaction zone, the gas having temperatures typically ranging fromambient temperature to below the thermal decomposition temperature(s) ofnitrates of manganese; contacting the gas in the second reaction zonewith sorbent for a time sufficient to primarily effect NO_(X) capture ata NO_(X) capture rate set point by formation of nitrates of manganese;and venting the gas substantially stripped of SO_(X) and/or NO_(X) andrendered free of reacted and unreacted sorbent from the second reactionzone.

In another embodiment, the process comprises providing a removal systemaccording to the invention, the removal system being comprised of atleast one feeder and a modular reaction unit as described above;introducing gas containing SO_(X) and NO_(X) into a first bag house ofthe modular reaction unit, the gas having temperatures typically rangingfrom ambient temperature to below the thermal decompositiontemperature(s) of sulfates of manganese; contacting the gas in the firstbag house with sorbent for a time sufficient to effect SO_(X) capture ata target SO_(X) capture rate set point by formation of sulfates ofmanganese; passing the gas substantially stripped of SO_(X) from thefirst bag house into a second bag house of the modular reaction unit,the gas having temperatures typically ranging from ambient temperatureto below the thermal decomposition temperature(s) of nitrates ofmanganese; contacting the gas in the second bag house with sorbent for atime sufficient to effect NO_(X) capture at a target NO_(X) capture rateset point by formation of nitrates of manganese; and venting the gassubstantially stripped of SO_(X) and NO_(X) and free of reacted andunreacted sorbent from the second bag house.

In another embodiment, the process further comprises the steps ofremoving reacted sorbent from reactions zones of a system of theinvention; washing the sorbent in a dilute acid rinse to dissolvesulfates and/or nitrates of manganese on the surface of sorbentparticles into solution and thereby cleaning the sorbent; separating thecleaned sorbent from the acid rinse; drying the cleaned sorbent; andpulverizing the cleaned sorbent to de-agglomerate the cleaned sorbent.

In another embodiment, the process further comprises the steps ofremoving reacted sorbent from reactions zones of a system of theinvention; washing the sorbent in a dilute acid rinse to dissolvesulfates and/or nitrates of manganese on the surface of sorbentparticles into solution and thereby cleaning the sorbent; separating thecleaned sorbent from the acid rinse; conveying the cleaned sorbent to adryer; drying the cleaned sorbent; conveying the cleaned sorbent to apulverizer; pulverizing the cleaned sorbent to de-agglomerate thecleaned sorbent; and conveying the de-agglomerated clean sorbent to thesorbent feeder for reintroduction into the system.

In another embodiment, the process further comprises the steps ofremoving reacted sorbent from reactions zones of a system of theinvention; washing the sorbent in a dilute acid rinse to dissolvesulfates and/or nitrates of manganese on the surface of sorbentparticles into solution and thereby cleaning the sorbent; separating thecleaned sorbent from the acid rinse to provide a filtrate containingdissolved sulfates and/or nitrates of manganese; adding alkali orammonium hydroxide to the filtrate to form an unreacted sorbentprecipitate of oxides of manganese and a liquor containing alkali orammonium sulfates and/or nitrates; separating the unreacted sorbentprecipitate from the liquor, the liquor being routed for furtherprocessing into marketable products or for distribution and/or sale as auseful by-product; rinsing the sorbent precipitate; drying the sorbentprecipitate to form unreacted sorbent; and pulverizing the unreactedsorbent to de-agglomerate the unreacted sorbent.

In another embodiment, the process further comprises the steps ofremoving reacted sorbent from reactions zones of a system of theinvention; washing the sorbent in a dilute acid rinse to dissolvesulfates and/or nitrates of manganese on the surface of sorbentparticles into solution and thereby cleaning the sorbent; separating thecleaned sorbent from the acid rinse to provide a filtrate containingdissolved sulfates and/or nitrates of manganese; adding alkali orammonium hydroxide to the filtrate to form a sorbent precipitate ofoxides of manganese and a liquor containing alkali or ammonium sulfatesand/or nitrates; separating the sorbent precipitate from the liquor, thesorbent precipitate being routed for regeneration of unreacted sorbent;and routing the liquor for distribution and/or sale as a usefulby-product or for further processing into marketable products.

In another embodiment, the process further comprises the steps ofremoving reacted sorbent from a reaction zone of the system whereprimarily NO_(X) capture occurred by reacting with the sorbent to formnitrates of manganese; heating the reacted sorbent to thermallydecompose the nitrates of manganese, to desorb NO₂, and to regeneratereacted sorbent to form unreacted sorbent of oxides of manganese; andfurther heating the unreacted sorbent in an oxidizing atmosphere tocomplete the regeneration of the sorbent.

In another embodiment, the process further comprises the steps ofremoving reacted sorbent from a reaction zone of the system whereprimarily NO_(X) capture occurred by reacting with the sorbent to formnitrates of manganese; heating the reacted sorbent to thermallydecompose the nitrates of manganese, to desorb NO₂, and to regeneratereacted sorbent to form unreacted sorbent of oxides of manganese;passing the evolved NO₂ through a wet scrubber containing water and anoxidant to form a nitric acid liquor; and routing the nitric acid liquorfor further distribution and/or sale as a useful product or on forfurther processing.

In another embodiment, the process further comprises the steps ofremoving reacted sorbent from a reaction zone of the system whereprimarily NO_(X) capture occurred by reacting with the sorbent to formnitrates of manganese; heating the reacted sorbent to thermallydecompose the nitrates of manganese, to desorb NO₂, and to regeneratereacted sorbent to form unreacted sorbent of oxides of manganese;passing the evolved NO₂ through a wet scrubber containing water and anoxidant to form a nitric acid liquor; adding an ammonium or alkalihydroxide to the acid liquor to form a liquor containing ammonium oralkali nitrates; and routing the liquor for distribution and/or sale asa useful by-product or for further processing into marketable products.

In another embodiment, the process further comprises the steps ofrremoving SO_(X) and NO_(X) reacted sorbent from a reaction zone of thesystem; heating the reacted sorbent to a first temperature to evolveNO₂, the desorb NO being routed for further processing and/or handling;and heating the reacted sorbent to a second temperature to evolveSO_(X), the evolved SO_(X) being routed for further processing and/orhandling and the reacted sorbent being regenerated to unreacted sorbent.

In another embodiment, the process further comprises the steps ofremoving NO_(X), SO_(X) and mercury reacted sorbent from a reaction zoneof the system; heating the sorbent to a first temperature to desorb NO₂which is routed for further processing into marketable products; heatingthe sorbent to a second temperature to desorb elemental mercury which isrouted to a condenser for recovery; rinsing the sorbent to wash away anyash and to dissolve sulfates of manganese into solution to form aliquor; separating any ash in the liquor, the separated ash being routedfor further handling; adding alkali or ammonium hydroxide to the liquorto form an unreacted sorbent precipitate of oxides of manganese and aliquor containing alkali or ammonium sulfates, the liquor containingrinsed sorbent; separating the rinsed sorbent and unreacted sorbentprecipitate from the liquor, the liquor being routed for furtherprocessing into marketable products or for distribution and/or sale as auseful by-product; drying the rinsed sorbent and sorbent precipitate toform unreacted sorbent; and pulverizing the unreacted sorbent tode-agglomerate the unreacted sorbent.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram showing a system according to theinvention.

FIG. 2 is a schematic block diagram showing a system according to theinvention.

FIG. 3 is a schematic block diagram showing a system according to theinvention.

FIG. 4 is a block diagram showing a system according to the invention.

FIG. 5 is a block diagram showing a system according to the invention.

FIG. 6 is a perspective view of a commercially available bag house.

FIG. 7 is an end elevation view of a commercially available bag house.

FIG. 8 is a top plan view of a commercially available bag house.

FIG. 9 is a side elevation view of a commercially available bag house.

FIG. 10 is a sectional view of an inverted bag house according to theinvention.

FIG. 11 is a top plan view of an inverted bag house according to theinvention.

FIG. 12 is a flow diagram of a bag house reactor according to theinvention.

FIG. 13 is a block diagram of a system according to the invention.

FIG. 14 is a block diagram of a system according to the invention.

FIG. 15 is a block diagram of a system according to the invention.

FIG. 16 is a flow diagram an electronic control system useful in theinvention.

FIG. 17 is electronic control panel display.

FIG. 18 is electronic control panel display.

FIG. 19 is electronic control panel display.

FIG. 20 is a block diagram of a control sub-element according to theinvention for regulating differential pressure.

FIG. 21 is a control sub-element according to the invention for controlof SO_(X) or NO_(X) capture rate or sorbent feed rate.

FIG. 22 is a control sub-element according to the invention for controlof bag house gas inlet temperature.

FIG. 23 is a control sub-element according to the invention for controlof variable venturi position(s).

FIG. 24 is a control sub-element according to the invention for controlof SO_(X) or NO_(X) capture rate, differential pressure, and sorbentfeed rate.

FIG. 25 is a control sub-element according to the invention for controlof SO_(X) or NO_(X) capture rate, differential pressure, sorbent feedrate, and variable venturi position.

FIG. 26 is a block diagram of a system and process according to theinvention.

FIG. 27 is a block diagram of a system and process according to theinvention.

FIG. 28 is a block diagram of system according to the invention.

FIG. 29 is a graph plotting NO_(X) values over time.

FIG. 30 is a graph plotting SO_(X) values over time.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to systems and processes for removal of SO_(X)and/or NO_(X) as well as other pollutants, from a gas stream. In theinvention, gas containing SO_(X) and/or NO_(X) is introduced into afirst reaction zone where the gas is contacted with a sorbent ofregenerable oxides of manganese and/or regenerated oxides of manganese.The sorbent may interact with the pollutants in a gas stream as acatalyst, a reactant, an absorbent or an adsorbent. The oxides ofmanganese react with the SO_(X) and the NO_(X) to form, respectively,sulfates of manganese and nitrates of manganese.

“Nitrates of manganese” is used herein to refer to and include thevarious forms of manganese nitrate, regardless of chemical formula, thatmay be formed through the chemical reaction between NO_(X) and thesorbent and includes hydrated forms as well.

Similarly, “sulfates of manganese” is used herein to refer to andinclude the various forms of manganese sulfate, regardless of chemicalformula that may be formed through the chemical reaction between SO_(X)and the sorbent and includes hydrated forms as well.

“Target pollutant(s)” means the pollutant or pollutants that aretargeted for removal in the system.

“Substantially stripped” means that a pollutant has been removed from agas at about a targeted capture rate whether by interaction with asorbent or physical removal in a solid-gas separator. With respect topollutants removed by interaction with a sorbent, it furthercontemplates that removal up to a targeted capture rate for thatpollutant may be commenced in a first reaction zone and completed in asubsequent reaction.

“Reacted sorbent” means sorbent that has interacted with one or morepollutants in a gas whether by chemical reaction, adsorption orabsorption. The term does not mean that all reactive or active sites onthe sorbent have been utilized since all such sites may not actually beutilized.

“Unreacted sorbent” means virgin sorbent that has not intereacted withpollutants in a gas.

Some of the reaction zones may also serve as solid-gas separatorsrendering the gas free of solids and particulates, such as sorbent,whether reacted or unreacted, fly ash, and mercury compounds, so as toallow the gas that is substantially stripped of SO_(X) and/or NO_(X) orother pollutants to be vented from the reaction zone and passed toanother reaction zone or routed up a stack to be vented into theatmosphere. The solids and particulates which include the reacted andunreacted sorbent, fly ash, and the like, are retained within reactionzones that are solid-gas separators and may be subsequently removed forfurther processing.

Reaction zones may be multi-stage removal systems which wouldincorporate additional reaction zones. The reaction zones utilized insingle stage, dual stage, or multi-stage removal may be a fluidized bed,a pseudo-fluidized bed, a reaction column, a fixed bed, a pipe/ductreactor, a moving bed, a bag house, an inverted bag house, bag housereactor, serpentine reactor, and a cyclone/multiclone.

The gases that may be processed in the invention are most gasescontaining SO_(X) and/or NO_(X). Such gases may be generated by thecombustion of fossil fuels in power plants, heating plants and variousindustrial processes, such as the production of taconite pellets bytaconite plants, refineries and oil production facilities, gas turbines,and paper mills. Combustion for heating and other process steps at suchfacilities generate waste or flue gases that contain SO_(X) and NO_(X)in various concentrations, typically but not limited to 500 ppm or lessfor NO_(X) and 3000 ppm or less for SO_(X). Further, the gases maycontain other removable pollutants, such as fly ash, and mercury (Hg),as elemental Hg in vapor form or mercury compounds in particulate form,in small concentration, e.g., 0.0047 ppm (4.7 ppb). The gases mayfurther contain hydrogen sulfide and other totally reduced sulfides(TRS) and other pollutants. These gases may typically have temperaturestypically ranging from ambient temperature to below the thermaldecomposition temperature(s) of nitrates of manganese and to below thethermal decomposition temperature(s) of sulfates of manganese. Gasesgenerally within this temperature range can be processed in the systemof the invention.

The primary sorbent useful in the invention are oxides of manganese,which may be found in manganese ore deposits or derived synthetically.Manganese compounds of interest occur in three different oxidationstates of +2, +3, and +4; this gives rise to a range of multivalentphases, which provide oxides of manganese with a great diversity ofatomic structures and thus mineral forms. Examples of these mineralforms include, but are not limited to, pyrolusite (MnO₂), ramsdellite(MnO₂), manganite (MnOOH or Mn₂O₃.H₂O), groutite (MnOOH), and vernadite(MnO₂.nH₂O) to name a few. This is reported by Jerry E. Post in hisarticle “Manganese Oxide Minerals: Crystal structures and economic andenvironmental significance,” Proc. Nat'l. Acad. Sci, U.S.A., Vol. 96,pp. 3447-3454, March 1999, the disclosure of which is incorporatedherein by this reference.

One of the most common of the various forms of oxides of manganese ismanganese dioxide, MnO₂. The pyrolusite form of this mineral is oftenthe primary mineral form in manganese deposits. Pyrolusite is composedpredominantly of the compound MnO₂. This oxide of manganese exhibits atleast two crystalline forms. One is the gamma form, which is nearlyamorphous. The other is a beta form that exhibits pronounced crystallinestructure. The term “oxides of manganese” as used herein is intended torefer and include the various forms of manganese oxide, their hydratedforms, and crystalline forms, as well as manganese hydroxide (e.g.Mn(OH)₂), etc.

With reference to the removal of SO_(X) and/or NO_(X), the relativecapture or removal efficiencies of oxides of manganese may be understoodby the below calculation(s) of loading rates. In order to assess theeconomics of the system and processes of the invention, it is necessaryto determine the gas removal efficiencies of the sorbent. Gas captureefficiency based upon test results may be calculated by dividing weightof gas removed by weight of sorbent. This provides an approximatepicture of system operations, but does not account for stoichiometry ofthe reactions or interference between reactive gases in a multiple-gassystem. The stoichiometric gas capture ratio is described below.

For the purpose of this assessment the overall reactions believed tooccur between the sorbent, oxides of manganese, and sulfur dioxide (SO₂)and nitric oxide (NO) are shown below, with molecular weights shownabove each species.

These reactions may occur in multiple steps. Molecular weights are shownabove each species. Based on these reactions, the theoretical maximumstoichiometric gas capture by weight of MnO₂ sorbent is the ratio of themolecular weights of the products versus the reactants which is 73% forSO₂ or 69% for NO, for systems containing only one reactive gas. For asystem containing two reactive gases, depending on reactioncharacteristics, the maximum stoichiometric gas capture will be lowerfor both gases. If reaction speeds are assumed to be equal for bothreactive gases, maximum stoichiometric gas capture for each gas shouldbe proportional to the percentage of each gas present.

For example, during a 48-hour test, two reactive gases, SO₂ and NO werepresent at approximately 430 ppm and 300 ppm, respectively. Totalweights of reactive inlet gases treated were:SO₂=98.45 lb. NO=47.02 lb. total=145.47 lb.Therefore, SO₂ and NO represented 67.7% and 32.3% respectively, ofreactive gases present. If the theoretical maximum stoichiometric gascapture for a single-gas system is corrected to these reactive gasweight proportions, the theoretical maximum percentage capture for eachgas by MnO₂ weight is:SO₂: (0.73 single-gas)×(0.67 for the 48-hr. test)=0.489=48.9%NO: (0.69 single-gas)×(0.323 for the 48-hr. test)=0.223=22.3%Therefore, the theoretical maximum weights of gases captured by 289 lb.,for example, of sorbent for the 48-hour test would be:SO₂: (289 lb. Sorbent)×(0.489)=141.4 lb. SO₂NO: (289 lb. Sorbent)×(0.323)=98.35 lb. NOActual gas capture experienced in the 48-hour test was 23.94 lb. of SO₂and 4.31 lb. of NO. For the 2-gas system, stoichiometric gas capturewas:SO₂: (23.94 lb. captured)/(141.4 lb. SO₂ possible)=16.9% (of theoreticalmaximum) NO: (4.31 lb. captured)/(64.41 lb. possible)=6.69% (of theoreticalmaximum)

Oxides of manganese, once reacted with SO_(X) and NO_(X) to formsulfates of manganese and nitrates of manganese respectively, can beregenerated. There are essentially two general methods of regeneration,thermal decomposition and chemical decomposition.

In thermal decomposition, the sulfates of manganese and/or nitrates ofmanganese are heated in an oxidizing atmosphere whereupon manganeseoxide is formed and nitrogen dioxide and/or sulfur dioxide are desorbedand captured. The captured nitrogen dioxide or sulfur dioxide can bereacted with other chemicals to produce marketable products.

In the chemical decomposition or regeneration of manganese oxide, thesulfates of manganese and/or nitrates of manganese are dissolved fromthe used sorbent in a dilute acidic aqueous slurry to which, afterseparation and recovery of the washed sorbent, other compounds such asalkali or hydroxides or carbonates may be added and manganese oxide isprecipitated out of solution and removed. The solution, now free ofoxides of manganese, can be routed on for further processing orproduction of marketable products such as alkali or ammonium sulfatesand nitrates. The regeneration of manganese oxide and production ofuseful or marketable products through thermal or chemical decompositionis further discussed below.

In the process of regeneration, the regenerated oxides of manganese arein particle form and are defined by the chemical formula MnO_(X), whereX is about 1.5 to 2.0. The regeneration process may be engineered toyield oxides of manganese having a particle size ranging from 0.1 to 500microns. Oxides of manganese in this range are useful in the invention.Preferably, the oxides of manganese will have a particle size of lessthan 300 microns, and more preferably of less than 100 microns. Theregenerable oxides of manganese and/or regenerated oxides of manganeseare typically fine, powdery, particulate compounds.

Reactivity of dry sorbents may generally be related to its particlesurface area. Particles or particulates all have weight, size, andshape, and in most cases they are of inconsistent and irregular shape.In the case of fine powders it is often desirable to know how muchsurface area a given quantity of powder exhibits, especially forparticles that are chemically reactive on particle surfaces, or are usedas sorbents, thickeners or fillers. (Usually measurements of surfacearea properties are done to compare several powders for performancereasons.) Particles may also have microscopic pores, cracks and otherfeatures that contribute to surface area.

The BET (Brunauer-Emmett-Teller) method is a widely accepted means formeasuring the surface area of powders. A powder sample is exposed to aninert test gas, such as nitrogen, at given temperature and pressures,and because the size of the gas molecules are known at those conditions,the BET method determines how much test gas covers all of the exteriorsurfaces, exposed pores and cracks with essentially one layer of gasmolecules over all of the particles in the powder sample. Optionally,the analyst can use other test gases such as helium, argon or krypton;and can vary from 1 to 3 relative test pressures, or more, for betteraccuracy. From this, a measure of total surface area is calculated andusually reported in units of square meters of particle surface area pergram of powder sample (m²/g). Generally, coarse and smooth powders oftenrange in magnitude from 0.001 to 0.1 m²/g of surface area, and fine andirregular powders range from 1 to 1000 m²/g. Since the interactionsbetween a sorbent and the pollutant occurs primarily at the surface ofsorbent particle, surface area correlates with removal efficiency. Theoxides of manganese useful in the invention are fine and irregularpowders and thus may have a surface area ranging from 1 to 1000 m²/g.Preferably the sorbent will have a surface area of greater than 15 m²/g,and more preferably of greater than 20 m²/g.

With reference to FIG. 1, a system according to the invention isillustrated in block diagram form. The system 10 may be seen ascomprised of a feeder 20 and a first reaction zone 30 and a secondreaction zone 38. The feeder 20 would contain a supply of sorbent ofregenerable oxides of manganese and/or regenerated oxides of manganese.The feeder 20 is configured to handle and feed oxides of manganese,which, upon regeneration, are in particle form and defined by thechemical formula MnO_(X) where X is about 1.5 to 2.0. The first reactionzone 30 is configured for introduction of the sorbent in a gascontaining SO_(X) and NO_(X). In one embodiment, the first reaction zone30 may be a section of pipe/duct, possibly configured as a fluidizedbed, a pseudo-fluidized bed, a reaction column, a fixed bed, a pipe/ductreactor, a moving bed, a bag house, an inverted bag house, bag housereactor, serpentine reactor, and a cyclone/multiclone. The secondreaction zone 38 a fluidized bed, a pseudo-fluidized bed, a reactioncolumn, a fixed bed, a pipe/duct reactor, a moving bed, a bag house, aninverted bag house, bag house reactor, serpentine reactor, and acyclone/multiclone. Preferably, the second reaction zone is a bag house,such as commercially available bag house, an inverted bag houseaccording to the invention, or a bag house reactor according to theinvention.

The gas containing SO_(X) and NO_(X), or other pollutants, comes from agas source 15 external to the system. The gas is introduced into thefirst reaction zone 30 and is contacted with sorbent introduced into thefirst reaction zone 30 from the feeder 20 and is contacted with thesorbent for a time sufficient to primarily effect SO_(X) capture at atargeted SO_(X) capture rate. For purpose of discussion, and not wishingto be held to a strict interpretation, with respect to effecting acertain capture, it has been observed that oxides of manganese can morereadily capture SO₂ in a gas stream absent of NO, and also can morereadily capture NO in a gas stream absent of SO₂, than when the gasstream contains both SO₂ and NO. SO_(X) capture tends to proceed at amuch faster rate than NO_(X) capture when the two pollutants are presentin a gas stream.

The gas and sorbent may be introduced separately or commingled beforeintroduction into a reaction zone. Once the gas and sorbent have beencontacted for sufficient time, the SO_(X) is captured by reacting withthe sorbent to form sulfates of manganese to substantially strip the gasof SO_(X). The gas substantially stripped of SO_(X) passes from thefirst reaction zone 30 into the second reaction zone 38. The secondreaction zone 38 is configured for introduction of sorbent and the gassubstantially stripped of SO_(X). In the second reaction zone 38, thegas is further contacted with sorbent for a time sufficient to primarilyeffect NO_(X) capture at a targeted NO_(X) capture rate. The NO_(X) iscaptured by reacting with the sorbent to form nitrates of manganese tosubstantially strip the gas of NO_(X). The second reaction zone 38 isfurther configured so that the gas which has been substantially strippedof both SO_(X) and NO_(X) is rendered free of reacted and unreactedsorbent. The gas may then be vented from the second reaction zone 38 toa stack 40 where the gas is released to the atmosphere.

Differential pressure across the reactor system is regulated by acontrol sub-element (not shown in FIG. 1) so that any differentialpressure across the system is no greater than a predetermined level. Asis later described, the control sub-element may control other systemparameters such as feeder rate, SO_(X) and/or NO_(X) capture rate, andthe inlet gas temperature into the reaction zones. Thus, the system ofthe invention is highly adaptable and, in another embodiment, isgenerally comprised of a feeder 20, a first reaction zone 30, a secondreaction zone 38, and at least one control sub-element for regulatingprocess parameters.

In another embodiment of the invention, the system is comprised of afeeder 20 as previously described and a modular reaction unit 60comprised of at least three interconnected reaction zones. Withreference to FIG. 2, where the reaction zones are three interconnectedbag houses 62, 64, 66, the modular reaction unit may be understood. Thebag houses 62, 64, 66 are connected so that a gas containing SO_(X)and/or NO_(X) can be routed through any one of the bag houses, any ofthe two bag houses in series, or all of the at least three bag houses inseries or in parallel or any combination of series or parallel. Each baghouse is separately connected to the feeder 20 and to the external gassource 15. Through these connections, sorbent and gas can be introducedinto each bag house where SO_(X) and NO_(X) capture can occur when thegas is contacted with sorbent for a time sufficient to allow formationof sulfates of manganese, nitrates of manganese, or both. The system inthis embodiment may also include control sub-elements 50 (not shown) forregulating various process parameters. The reaction zones of the modularunit 60 are not limited to bag houses and may be any combination ofreaction zones useful in the inventory. If the bag houses are operatedindependently of each other, then the section of pipe or duct(pipe/duct) preceding the bag house and that which is connected to aninlet of each bag house conveys gas into each bag house and is alsoconfigured as a first reaction zone 30, a pipe/duct reactor, into whichgas containing SO_(X) and NO_(X) flows along with the sorbent. The gasis mixed with the sorbent in the pipe/duct reactor for a sufficient timeto achieve SO_(X) capture at a targeted capture rate. In this mode, thesystem operates as illustrated in FIG. 1 with each bag house 62, 64, 66being a second reaction zone 38 into which the gas that has beensubstantially stripped of SO_(X) passes from the first reaction zone 30,pipe/duct reactor.

With reference to FIG. 3, another embodiment of the invention is shown.In this embodiment, the system 10 is comprised of a feeder 20, and threebag houses 70, 76, and 78, a common conduit 73 and a diverter valve 74.Gas and sorbent are introduced into the first bag house 70 which servesas a first reaction zone of a two-staged SO_(X)/No_(X) removal systemwhere primarily SO_(X) capture occurs. The gas substantially stripped ofSO_(X) then passes from the first bag house 70 into the common conduit73. As shown in FIG. 3, the common conduit 73 is Y-shaped, but may be ofany shape that allows gas to flow from the first bag house 70 and to bedirected to the second and third bag houses 76, 78 which each functionas the second reaction zone of a two-staged SO_(X)/NO_(X) removalsystem.

In the Y-shaped common conduit 73 can be seen a diverter valve 74illustrated as a dotted line at the fork of the “Y”. The diverter valve74 is positioned in the common conduit 73 so as to direct the flow ofgas from the first bag house 70 to the second bag house 76 and/or thethird bag house 78. The diverter valve 74 has variable positions, in thefirst position gas from the first bag house 70 is directed to the secondbag house 76, in the second (variable) position gas from the first baghouse 70 is directed to both the second and third bag houses 76,78, andin the third position, as illustrated in FIG. 3, the gas from the firstbag house 70 is directed to the third bag house 78. Gas exiting thesecond and third bag houses 76 and 78 may be vented and directed forfurther processing or handling (e.g. directed to stack 40 or directed toa subsequent reactor for Hg removal). The system of this embodiment mayincorporate any combination of the reaction zones useful in theinvention and is not intended to be limited to bag houses.

However, when the reaction zones are bag houses, the system illustratedin FIG. 3 may further comprise an off-line loading circuit 42. Theoff-line loading circuit 42 is brought into use after the filter bagshave been pulsed to clean them of filter cake so reacted sorbent can beremoved for recycling or regeneration. There may be more than oneoff-line loading circuit 42, as shown in FIG. 3, each separatelyconnected to a bag house 76 and 78. The off-line loading circuit isconnected to a sorbent feeder and a bag house via an off-line loadingcircuit conduit 44 and incorporates a fan 46 for blowing air commingledwith sorbent into the bag houses 76 and 78 in order to pre-load thefabric filter bags in the bag houses by building a filter cake thereon.The air passing through the bags and cake thereon is vented from the baghouse. When the bag house is ready to come back on line, the off-lineloading circuit can be closed or switched off and the diverter valve 74moved to a position to permit the flow of process gas through the baghouse that is being brought back on line.

When NO_(X) is captured by the sorbent, the sorbent may not becompletely loaded or spent thus having remaining reactive sites. Eventhough it may no longer be effective as an efficient sorbent for NO_(X)at this point, the sorbent may have reactive sites that could beutilized efficiently for SO_(X) capture. Thus, the partially loadedreacted sorbent or NO_(X)-reacted sorbent in a second reaction zone of atwo-stage SO_(X)/NO_(X) removal system could be removed from the secondreaction zone and fed into the first reaction zone to allow additionalSO_(X) capture with, or loading onto, the sorbent. This would decreasethe frequency at which sorbent regeneration is needed and reduce theamount of virgin or unreacted sorbent that would need to be introducedinto the first reaction zone.

With reference to FIG. 4 a system according to the invention utilizingcounter-flow feed of NO_(X)-reacted sorbent is illustrated in a blockflow diagram. The system 10 is comprised of a first reaction zone 30, asecond reaction zone 38, a feeder 20 containing virgin or unreactedsorbent, and a NO_(X)-reacted sorbent feeder 21. The first reaction zone30 of system 10 is connected to external gas source 15 and gas flowsfrom the external gas source 15 to the first reaction zone 30, from thefirst reaction zone 30 to the second reaction zone 38, and from thesecond reaction zone 38 is either vented to stack 40 or directed on toanother system unit such as a mercury-sorbent reactor (not shown). Thefeeder 20 can feed virgin or unreacted sorbent into the first reactionzone 30 and the second reaction zone 38. NO_(X)-reacted sorbent isremoved from the second reaction zone and is conveyed from the secondreaction zone to the first reaction zone via NO_(X)-reacted sorbentfeeder 21 where the NO_(X)-reacted sorbent with available reaction sitesis further contacted with a gas containing both SO_(X) and NO_(X) toremove and capture SO_(X).

Using reacted sorbent feeders allows sorbent to be recycled to areaction zone where unreacted sites on the surface of the sorbent can beutilized. Through the mechanical operations of removing reacted sorbentfrom a reaction zone and returning it to the same or another reactionzone, the amount of virgin or unreacted sorbent that has to beintroduced into the system is reduced. A sorbent may be recycled thisway several times before regeneration is necessary due to the reductionin available reaction sites on the surface of sorbent particles. Thisrepresents significant cost savings and more economical and complete useof the sorbent.

During operation, the surfaces of sorbent particles may becomeobstructed, for example, by compaction or agglomeration. The physicalmanipulation and handling of the reacted sorbent re-orients theparticles making unexposed surfaces available to capture targetedpollutants.

The recycling of reacted sorbent in this way may proceed as shown inFIG. 4 in a counter-flow manner as discussed above. Recycling may alsoproceed by removing reacted sorbent from a reaction zone conveying it toa reacted sorbent feeder and introducing or re-introducing the reactedsorbent into the same reaction zone. This is shown in FIG. 28, wherereacted sorbent feeder 21A receives reacted sorbent conveyed from thefirst reaction zone 30 and reacted sorbent from reacted sorbent feeder21A is re-introduced into the first reaction zone 30. Further, reactedsorbent from second reaction zone 38 is conveyed to reacted sorbentfeeder 21B and re-introduced into the second reaction zone 38. This maybe desirable where a first targeted pollutant is being captured in thefirst reaction zone and a second targeted pollutant is being captured inthe second reaction zone. If, for example, SO_(X) is being captured inthe first reaction zone 30, the SO_(X) reacted sorbent when it is spentor ceases to be effective for SO_(X) removal, can then be routed forregeneration and recovery of sulfates as alkali or ammonium sulfate,useful commercial product. Similarly, if NO_(X) is the pollutant beingcaptured in the second reaction zone 38, the NO_(X) reacted sorbent canbe removed when it ceases to be effective for NO_(X) removal anddirected for regeneration and recovery to produce alkali or ammoniumnitrates, again, useful commercial by-products.

Capture rates may be affected by the gas inlet temperature as it entersa reaction zone and may need to be adjusted, cooled or heated to achievea desired capture rate for SO_(X) and/or NO_(X). This can beaccomplished with a heat exchanger. As is illustrated in FIG. 5, thesystem may further include a heat exchanger preceding each reaction zoneof a system of the invention. In FIG. 5, the system of the invention asillustrated is substantially the same as the illustration of FIG. 1,depicting first and second reaction zones 30 and 38, feeder 20, externalgas source 15, and stack 40. In FIG. 5, heat exchangers 72A, 72B havebeen introduced into the system before each reaction zone. The heatexchangers 72A, 72B may be utilized to heat or cool the gas stream priorto entry into each reaction zone. As the gas enters into the system, ifthe gas temperature is above the thermal decomposition temperature(s) ofeither sulfates of manganese or nitrates of manganese, the heatexchangers 72A, 72B will operate to cool the gas to a desiredtemperature based upon whether SO_(X) capture or NO_(X) capture is theprimary pollutant captured in the reaction zone. Similarly, if the gaswere below a desired temperature set point, the heat exchangers 72A, 72Bwill operate to heat the gas to the desired temperature. The heatexchangers 72A, 72B may be a gas-to-gas cooler or a heater unit, orother suitable means for accomplishing heating and cooling of gases toassure that the gas inlet temperature at a targeted temperature orwithin an acceptable range.

As previously mentioned above, the gases entering the system fromexternal gas source 15 may be any of a variety of process or industrialgases. These gases when generated encompass a range of temperatures. Dueto simple economics and the design of various plants and facilities forefficient use of waste heat which is captured or transferred to provideheat for various processes at a facility, these process gases willtypically have a temperature ranging from 250° F. to 350° F. or 120° C.to 180° C. In less typical situations, these gases may have temperaturesupwards of 1000° F., or 540° C. Gases at these temperatures are readilyprocessed in the systems of the invention and the heat exchangers 72A,72B can be utilized to maintain the gas within these temperature rangesif desired. The system can also process gases at much highertemperatures such as 1000° F. For purposes of SO_(X) and NO_(X) capture,the gas temperature should not exceed, respectively, the thermaldecomposition temperature(s) of sulfates of manganese and nitrates ofmanganese. Given that different forms or species of these sulfates andnitrates, the thermal decomposition temperature would depend upon thespecies formed during capture. It has been reported that that sulfatesof manganese may thermally decompose at temperatures approximating 950°C. Similarly, nitrates of manganese are believed to thermally decomposeat temperatures ranging up to 260° C. The system of the invention canprocess gases approaching these thermal decomposition temperatures. But,more typically, the system in practice will be operated in temperatureranges approximating those of process gases from industrial sources.

Heat or waste heat from the process gases of a facility may be utilizedin the regeneration and recovery processes discussed herein below.Further, the waste heat may be utilized for purposes of sorbentpreheating which serves to “activate” sorbent prior to introduction intoa reaction zone. Although the exact mechanism of activation is notknown, it is generally known that oxides of manganese can be “activated”with heat. Thus, as can be seen in FIG. 28, a system according to theinvention may further include a sorbent preheater 22 which may actuallybe part of or separate from sorbent feeder 20. The source of heat forthe sorbent preheater may be any heat source, but waste heat fromfacility processes can be economically efficiently utilized for thispurpose.

The SO_(X) and/or NO_(X) capture rate may be regulated by the amount ofsorbent fed into the reaction zones. In order to regulate capture rate,gas measuring devices, such as continuous emission monitors (CEMS), areutilized to measure the composition of the gas at the inlet to thereaction zone and at the outlet of the reaction zone. With reference toFIG. 14, the gas flows from the external gas source 15 and past CEMS 80Awhere the gas composition is measured prior to entry into first reactionzone 30. Another CEMS 80B is provided after the first reaction zone 30to measure the concentration of the gas substantially stripped of SO_(X)and/or NO_(X) as it passes from the first reaction zone 30. As in FIG.1, the gas may be vented to a stack 40, passed to a second reaction zone38, or another system unit for further processing.

In the system of the invention, a bag house may serve as a reaction zoneand/or as a solid gas separator, since bag houses are solid-gasseparators. A conventional, commercially available bag house 82 isdepicted in FIGS. 6 through 9. FIG. 6 is a perspective view of a baghouse 82. FIG. 7 is an end elevation view showing a bag house 82. FIG. 8is a top plan view of a bag house 82. FIG. 9 is a side elevation view ofa bag house 82. Within the bag house 82 are a plurality of bags 88 alsoreferred to as filter fabric bags shown in FIGS. 7 through 9. As can beseen in FIGS. 7 through 9, the bag house 82 has a plurality of filterfabric bags 88 suspended therein. Typically, they are suspended from aframe or support structure at the top of the bag house 82. The filterbags 88 may be of various shapes, e.g., conical or pyramidal, andinclude an internal frame and suitable fabric filter. Those skilled inthe art would be able to select suitable filter fabric materials fromthose commercially available. Gas and entrained sorbent enters the baghouse 82 through the bag house inlet 92, shown in FIGS. 7 through 9, andby virtue of an applied differential pressure, gases are forced throughthe fabric of the bags 88 and the entrained sorbents are separated fromthe gas by forming a filter cake on the surface of the bags 88. Thefilter cake thus formed is a reaction medium where pollutants arecontacted with and removed by the sorbent. The commingled gases andsorbents move vertically upward and contact the fabric and/or the filtercake formed thereon. The bags 88 are configured to permit the gases tobe directed from the outside to the inside of the bags to a conduit atthe top of the bag house 82 and then to the bag house outlet 98, shownin FIGS. 6 through 9.

While the bag house 82 is in operation, the filter bags 88 may beperiodically pulsed or otherwise agitated in order to adjustdifferential pressure across the bag house 82, which frees some or allof the filter cake and allows gas to flow more freely through the filtercake and the fabric filter bags. If the filter cake is allowed to gettoo thick, excess differential differential pressure across the baghouse or the system of the invention may result. Thus, the pulseintensity or frequency can be utilized to regulate or adjustdifferential pressure. When the bag house 82 is taken off line, the bags88 may be pulsed to free the bags 88 of virtually all reacted andunreacted sorbent not otherwise removed during normal operations. Thereacted and unreacted sorbent or filter cake fall from the bags 88 bygravity into a hopper 112 (seen in FIGS. 7 and 9) at the bottom of thebag house 82 for subsequent removal from the bag house hopper 112.Removal from the hopper 112 may be accomplished with a screw conveyor orby other appropriate means, even manually.

A thicker filter cake will lead to increased removal efficiency, but atthe price of extra power required to force the external gas sourcethrough the reaction zone. In one example, more power is required for aninduction fan to pull exhaust gases through the bag house when thefilter cake thickness is greater. The differential pressure may thus bemaintained at an optimal level, trading off increased power requirementsagainst the increased pollutant removal. In addition, the thicker thefilter cake the longer the residence time of the sorbent material in thesystem. Longer residence time of the gas in the filter cake results inbetter removal efficiencies. Higher sorbent loading rates results inless material that will have to be regenerated. This may also be takeninto consideration in setting the differential pressure set point.

In FIGS. 7 and 9, the plurality of filter bags is shown in positionwithin the bag house. Also shown near the top of the bag house 82 is apulse valve 124 utilized to pulse the fabric bags 88 in order to reducefilter cake thickness or to free the filter cake from the bags 88. Thebag house may be provided with a number of pulse valves 124. Duringoperation, these pulse valves 124 may be activated sequentially orrandomly in order to pulse the bags 88 in order to regulate and controldifferential pressure across the bag house 82 or the system as a whole.When the bag house is taken off-line, the bags may be pulsed to free thebags of virtually all filter cake so that reacted and unreacted sorbentmay be removed.

The bag house illustrated in FIGS. 6 through 9 is of a conventionaldesign. In FIGS. 10 and 11, a novel bag house according to the inventionis illustrated. This bag house, which can be utilized in the system ofthe invention, is referred to as an inverted bag house 140. The invertedbag house 140 eliminates the need for high can velocities, and permitsdownward, vertical flow of gases and reacted and unreacted sorbent. Theinverted bag house 140 is comprised of a bag house housing 142, at leastone inlet 145, a plurality of fabric filter bags 88, a support structure149 for the filter bags, a hopper 152 to receive and collect reacted andunreacted sorbent, an outlet 154, and a conduit 158. The bag househousing permits the introduction of gases and reacted and unreactedsorbent entrained in the gases, has a top and a bottom and is configuredfor gases to flow vertically downward from the top to the bottom of thebag house. The inlet 145 is located near the top of the bag househousing and is configured for the introduction of gases and reacted andunreacted sorbent entrained in the gases into the bag house. Theplurality of fabric filter bags 88 are configured to allow gas to flowfrom the outside of the bags 88 to the inside of the bags 88 under anapplied differential pressure and to prevent the passage of reacted andunreacted sorbent from the outside to the inside of the bags 88, therebyseparating reacted and unreacted sorbent from the gas and forming afilter cake on the bags 88. The support structure 149 is configured toreceive and support the fabric filter bags 88 and to provide openingsthrough which reacted and unreacted sorbent may be freely passeddownward into the hopper 152 by gravity. The hopper 152 is configured toreceive the reacted and unreacted sorbent and to permit the removal ofthe reacted and unreacted sorbent. The inverted bag house 140 also hasan outlet 154 located near the bottom of the housing 142 below the bags88 and above the hopper 152. The outlet 154 is connected to a conduit158 located below the fabric filter bags 88 and positioned to receivegas passing through the fabric filter bags. Conduit 158 conveys gas tothe outlet so that the gas may be vented or passed from the inverted baghouse 140.

In FIG. 12, a bag house reactor 150 of the invention is illustrated.This bag house reactor 150 can also be utilized in the system in placeof a conventional bag house. The bag house reactor 150 has interiorsurface 154 and exterior surface 152. It may be viewed as having anupper section 156, central section 157 and lower section 158. Generallylocated in the central and/or lower sections 157, 158 is a variableventuri 160. The purpose of the variable venturi 160 is to adjust thevelocity of gas flowing through the venturi opening within the bag housereactor 150. The variable venturi 160 is configured to adjust theposition of the variable venturi by varying the space or distancebetween the variable venturi 160 and the interior surface 154 of the baghouse reactor 150. In order to vary position a variable venturi positiondetector 367 shown in FIG. 23) for determining the position of thevariable venturi 160 and a variable venturi positioner 368 (shown inFIG. 23) for adjusting the position of the variable venturi 160 areprovided.

With the variable venturi 160 contacting the interior surface 154 of thebag house reactor 150, gas cannot flow from the lower section 158 to thecentral and upper sections 156, 157 of the bag house. By opening thespace between the variable venturi 160 and the interior surface 154, gasis allowed to flow through the reactor 150. Gas introduced through gasdistribution conduit 164 and the gas distribution port 162 flows fromthe lower section 158 to above the variable venturi 160 and into thecentral and upper sections 156, 157, and to the filter bags 88. When thespace between the variable venturi 160 and the interior surface 154 iswide, the gas flows at lower velocities which allows some of the sorbentsuspended above the variable venturi 160 to fall into the hopper 112.

There is also a sorbent distribution port 166 connected to a sorbentfeed conduit 168. The sorbent distribution port 166 is positioned abovethe variable venturi 160 to allow the introduction of sorbent into theupper section 156 of the bag house reactor 150. The sorbent distributionport 166 is configured to allow introduction of sorbent into the baghouse. Port 162 is configured to allow introduction of gas into the baghouse reactor.

The bag house reactor 150 has a plurality of fabric filter bags 88secured therein. The fabric filter bags are mounted in the upper section156 of the bag house reactor 150 and extend downward into the centralsection 157. At the bottom of the bag house reactor in the lower section158, is a sorbent hopper 112 where reacted and unreacted sorbent iscollected. The sorbent hopper is connected to outlet 172. Outlet 172 hasan outlet valve 176 which in the open position allows for the removal ofsorbent from the hopper 112. A vent 180 is located in the top section156 of the bag house reactor 150. Gases flowing through the bag housereactor 150 pass from the bag house reactor 150 through the vent 180 andmay be directed on for further processing or venting to the atmosphere.

Sorbent entrained in gases containing pollutants such as SO_(X) andNO_(X) can begin reacting with the sorbent during transport in thesorbent feeder conduit 168. Since SO_(X) is more reactive than NO_(X),the more reactive SO_(X) is primarily captured while it is beingtransported to the bag house reactor 150 in the first sorbent feederconduit 164. At lower gas velocities the larger solids will abrade intofiner solids and re-fluidize. The finer solids will travel upwardthrough the opening between the variable venturi 160 and the interiorsurface 154 where the sorbent is suspended to create a pseudofluidized-bed above the variable venturi 160 and the finest particuleswill travel upwards to form a filter cake on the surface of the fabricfilter bags 88. By adjusting the position of the variable venturi 160increasing or decreasing the space between the variable venturi 160 andthe interior surface 154 of the bag house reactor 150 gas velocity iscorrespondingly decreased or increased. In operation, the variableventuri may be positioned to achieve a gas velocity sufficient tosuspend a selected coarse fraction sorbent just above the orifice tocreate a pseudo-fluidized bed which may primarily or preferentiallycapture SO_(X), since SO_(X) is more reactive than NO_(X). Partiallystripped gas flows upward from the pseudo-fluidized bed carrying thefiner fraction sorbent onto the filter bags. The resulting filter cakeprovides a reaction medium where “slower” reactions, such as NO_(X)removal may occur. The variable venturi 160 position may be adjusted toachieve the desired thickness of filter cake on the fabric bags 88thereby increasing or decreasing the differential pressure across thesystem also to balance overall differential pressure by changing theventuri restriction. The fabric filter bags 88 may also be pulsed topartially remove filter cake and thus regulate differential pressure.The gas flow rate entering port 162 can be adjusted to regulate upwardgas velocity so that the bags 88 may be pulsed to allow some of theloaded sorbent to fall into the hopper 112 without being reentrained inthe gas or redeposited on the bags 88.

Using the variable venturi 160, one can operate the system so thatsorbent suspended above the venturi, loaded with the faster reactinggases, can primarily be captured by falling to the hopper before beingcarried up to the filter bags 88. The fraction of sorbent loaded withfaster reacting gases can then be removed from the hopper 112 by openingthe outlet valve 176 so that that fraction may be removed from thehopper 112 through the outlet 172. Later the fabric filter bags 88 canbe pulsed to release the sorbent loaded with slower reacting gases whichwould then fall through the variable venturi 160 into the hopper 112.The sorbent loaded with slower reacting gases could then be removed fromthe hopper through loaded sorbent outlet 172 after the outlet valve 176has been opened. This could allow for the separate processing of thedifferent loaded sorbent fractions to regenerate the sorbent and produceuseful by-products.

Differential pressure, which represents sorbent filter cake thickness,is only one of several process parameters that can be controlled in thesystem in order to achieve desired levels of SO_(X) and NO_(X) removalefficiencies and cost advantages of the system. NO_(X) and SO_(X)removal efficiency may be regulated by various processes, includingsorbent feeder rate and temperature control at the inlet to the reactionzones of the system. These controls are achieved by the controlsub-elements or electronics, which include hardware and software andalso are referred to herein below as control loops.

Referring now to FIG. 13, a differential pressure control loop 300 isillustrated. External gas source 15 is illustrated feeding firstreaction zone 30, which in turn feeds generally an output gas stream316, which can feed either stack 40 or second reaction zone 38. Thedifferential pressure across first reaction zone 30 may be measured asillustrated as difference in pressure between the inlet pressure 306 andthe outlet pressure 304. In the example illustrated, inlet pressure 306and outlet pressure 304 feed a differential pressure cell 308, whichsends a differential pressure signal 310 to a differential pressurecontroller 302.

Differential pressure controller 302 can be any appropriate controller,including a proportional integral derivative (PID) controller. As usedherein, PID controllers may be understood to operate using anycombination of the proportional, integral, and derivative components.Differential pressure controller 302 can accept a set point 312,indicating the desired differential pressure across first reaction zone30. Set point 312 can be human or computer generated. As discussedbelow, differential pressure controller 302, and other controllers, maybe implemented as a stand-alone controller, distributed control system,as a PID block in a programmable logic controller (PLC), or as a set ofdiscrete calculations within a PLC. Differential pressure controller 302generates an output signal or output 314 to control the differentialpressure across first reaction zone 30. In embodiments where firstreaction zone 30 includes a bag house or uses solids-filtering media,differential pressure controller 302 output signal 314 may control theshaking, pulsing, or other removal of sorbent which has formed a filtercake on the filter medium.

In one embodiment, first reaction zone 30 includes numerous filter bagswhich can have an exterior containing sorbent material and an interiorhaving a lower pressure, acting to pull the sorbent material against thebag filter media. In one example of the invention, a compressed air jet,pulse valve 124, is periodically discharged within the interior of thefilter. In one embodiment, the compressed air pulse is sufficientlystrong to dislodge a portion of caked sorbent material from the filtermaterial even during normal operation of the bag house, not requiringthe shut down of the bag house. In one embodiment, the individual bagsare sequentially pulsed to dislodge a portion of caked sorbent material.The frequency of the pulsing may be increased in order to maintain athinner filter cake thickness. Thus, increasing the frequency of theperiodic pulsing of each filter bag will maintain a smaller filter cakethickness, and thus result in a smaller differential pressure across thebag house as a whole. In one embodiment, filter bags are grouped by row,with each row periodically pulsed at the same instant. In someembodiments, output 314 from differential pressure controller 302includes a frequency for pulsing filters within a bag house reactionzone. Differential pressure controller 302, in response to a higherdifferential pressure than set point, may increase the frequency offilter pulsing through output 314. Conversely, in response to a lowerdifferential pressure than set point, differential pressure controller302 may decrease the frequency of filter pulsing through output 314.

In one embodiment, the individual filter bags are formed of cylindricalfilter media disposed about a rigid cylindrical cage, with thecompressed air jet, pulse valve 124, disposed within the cylindricalrigid cage. After a period of time, the sorbent material filter cakebuilds up on the outside of the filter media, forming a thick filtercake. The pulsed air jet can force the filter media momentarily awayfrom the cylindrical rigid cage, thereby cracking the caked sorbentmaterial and dislodging it, thereby allowing the sorbent material tofall under gravity to be collected and removed from the reaction zone.

A thicker filter cake can lead to increased pollutant removalefficiency, but at the price of extra power required to force theexternal gas source through the reaction zone. In one example, morepower is required for an induction fan to pull exhaust gases through thebag house when the filter cake thickness is greater. The differentialpressure may thus be maintained at an optimal level, trading offincreased power requirements against the increased pollutant removal. Inaddition, as the filter cake thickness increases the contact orresidence time of the gas with sorbent material in the system increases,resulting in more complete reaction. Therefore less material will haveto be regenerated. This may also be taken into consideration in definingthe differential pressure set point.

Referring now to FIG. 14, an emissions control loop 320 is illustrated.A gas stream may be seen to flow from gas source 15, through a firstcontinuous emission monitor system (CEM) 80A, then to first reactionzone 30, then to a second CEM 80B. A sorbent feeder 20 may be seen tofeed material to first reaction zone 30. Feeder 20 may be a screw feederhaving a variable speed screw, auger, pneumatic conveyor, or othermethod to move sorbent, within.

CEM 80A and CEM 80B can represent a NO_(X) analyzer and/or SO_(X)analyzer. In one embodiment, CEM 80A is a chemiluminescent monitor, forexample, Thermo Electron model 42H. In one embodiment, CEM 80A includesa SO_(x) monitor such as Bovar Western Research model 921NMP, utilizinga spectrophotometric method. In some embodiments, CEM 80A and CEM 80Binclude both NO_(X) and S0 _(X) analyzers. A feed controller 322 may beseen to accept a first input 328 from an outlet CEM signal 325.Controller input 328 may be used as a feedback signal to control thefeeder rate. In some embodiments, a feeder controller 322 also has asecond input 330 accepting an inlet measurement signal 324, alsoincluding pollutant concentration data. Second input 330 may be used todisplay the incoming gas concentrations and/or to calculate percentageremoval set points in the system. Feeder controller 322 also accepts aset point signal 326, indicating the desired feed rate and/or thedesired NO_(X) or SO_(X) concentration exiting first reaction zone 30.Feeder controller output 332 can be a variable frequency drive signal,among other available signals, to control the speed of feeder 20.

Feeder controller 322 may be any suitable controller, including a PIDcontroller utilizing any combination of its individual modes. In oneembodiment, set point 326 is set at a desired concentration for eitherNO_(X) or SO_(X), depending on the embodiment. The gas concentrationsignal 325 from CEM 80B can be used by feeder controller 322 tocalculate output signal 332. When the gas concentration is higher thanindicated as desirable by set point 326, output 332 can be increased toincrease the speed of feeder 20, which will put more sorbent into firstreaction zone 30, thereby dropping the pollutant concentration.Conversely, when pollutant gas concentration 325 is lower than required,feeder controller output 332 can be decreased to decrease the rate ofsorbent addition from feeder 20 into first reaction zone 30.

Referring now to FIG. 15, the gas to be cleaned may be seen to flow fromexternal gas source 15, through a first heat exchanger 72A, throughfirst reaction zone 30, through second heat exchanger 72B, through asecond reaction zone 38, and to stack 40. FIG. 15 illustrates a systemhaving two reaction zones and two heat exchangers. The temperature tothe first reaction zone 30 may be seen to be controlled by a firsttemperature controller 340, which accepts a set point 344 and atemperature input 342, and generates an output 346 to first heatexchanger 72A. As previously discussed, the maximum desired temperaturein the reaction zone may depend on the thermal decompositiontemperature(s) of the sulfates of manganese or nitrates of manganese,depending on whether NO_(X) and/or SO_(X) are being removed. Lowertemperature set points will be above the dew point of the system andadjusted automatically or manually as needed. In one embodiment, thetemperature to be controlled is measured at the reaction zone itself,rather than at the outlet from the heat exchanger, in order to moredirectly measure the temperature in the reaction zone. In oneembodiment, temperature controller 340 output 346 may be a variableanalog signal or other variable signals used to control a variable speedblower to control the outlet temperature from heat exchanger 72A.Temperature controller 340 may increase/decrease the cooling air passingthrough heat exchanger 72A when the temperature in first reaction zone30 is greater/less than set point 344.

A second temperature controller 350 may be seen to accept a temperatureinput 352 from second reaction zone 38 and a set point 354, and togenerate an output 356 for heat exchanger 72B. Second temperaturecontroller 350 may be similar to first temperature controller 340. Inone embodiment, heat exchanger 72B is used to cool the incoming gas,using ambient air as the cooling medium. As discussed previously withrespect to temperature controller 340, second temperature controller 350may increase/decrease the output to a variable speed drive coupled to ablower when the temperature of second reaction zone 38 is greater/lessthan set point 354.

FIG. 15 also illustrates how a first feeder 20A may feed material tofirst reaction zone 30. A second feeder 20B may be used to feed sorbentmaterial to second reaction zone 38. First feeder 20A and second feeder20B may be controlled as previously described with respect to feeder 20in FIG. 14.

Referring now to FIG. 16, a control and data acquisition system 400 forcontrolling and monitoring the previously described processes isillustrated. System 400 may be seen to include generally a programmablelogic controller (PLC) 402 and a local on-site computer 440. Both PLC402 and local computer 440 may be coupled to the World Wide Web 424. PLC402 and local computer 440 may be accessed over World Wide Web 424 by auser PC 428, a hand-held computer such as a Palm Pilot™ 430, and otherdevices 426 which can access World Wide Web 424.

PLC 402 may be seen to include a PLC rack 403. In one example, PLC 402is an Allen-Bradley™ PLC. In one example, the Allen-Bradley™ PLC is aPLC 5. PLC rack 403 may be seen to include a PLC processor module 408,and Ethernet module 410, and a DC power supply 412. PLC 402 may be seento include an input/output bus 406, for example a Controlnet™ bus 406,and input/output bus 414, shown as Data Highway Plus™ 414, which isconnected to local programming computer 416. Bus 406, in the presentexample, may be seen to be coupled to numerous input/output cards 404.Input/output cards 404 may be seen to include a discrete I/O cards 404A,mixed discrete and analog I/O cards 404B, discrete I/O cards 404C,discrete and analog I/O cards 404D, more discrete and analog cards I/O404E, a variable frequency drive card 404F, and a second variablefrequency drive card 404G. The discrete I/O may be commonly used toaccept inputs from discrete switches such as limit switches, and theoutput used to open and shut valves and to start and stop motors. Theanalog I/O may be used to accept input analog measurements from sensorsand to control variable position output devices. The variable frequencydrive outputs may be used to control variable speed motors, for example,variable speed motors used to control airflow pass the heat exchangers.

PLC 402 may be seen to be coupled to an Ethernet hub 420 via an Ethernetcable 418. In one embodiment, a DSL modem 422 enables Ethernet hub 420to be accessed from World Wide Web 424. Local computer 440 may also beseen to be coupled to Ethernet hub 420 via an Ethernet cable 444.Ethernet cable 444 can be coupled to an Ethernet card 446. Similarly,local computer phone line 442 may be coupled to a PC modem card 450. ThePC modem card can provide access to World Wide Web 424 when a DSL modemline is not available or is not functioning. Local computer 440 may beseen to include software or software component 448 which can include,for example, Microsoft Windows 2000™ as an operating system that isproviding both server and terminal functionality. Software component 448can include an Allen-Bradley™ OLE Process Control (OPC) module 452, aswell as an Intellution™ OPC server component 454. The IFIX processmonitoring and control package by Intellution™ is used in oneembodiment. An Intellution™ process database component 456 may also beincluded. Allen-Bradley™ OPC server 452 can provide communicationbetween local on-site computer and Allen-Bradley™ PLC 402.

Intellution™ OPC server 454 can provide communication between theAllen-Bradley™ inputs and outputs and the Intellution™ processmonitoring and control system residing within local computer 440.Intellution™ process database 456 may be used to monitor and control theentire process. Intellution™ Work Space 458 may be used to allow accessto monitor, display, and change current data, and a historical data area460 may be used to trend historical process data. An Access™/Oracle™ RDBcomponent 462 may also be included to provide database reporting. In oneembodiment, a report module, for example, a Microsoft Excel™ or Crystal™report component 464 may also be provided. In some embodiments, anIntellution™ web server component 466 is provided, as is a Microsoft™Internet Information Server (IIS) module 468. In some embodiments, localon-site computer 440 has a local terminal or CRT as well to display,monitor, and change data residing in the Intellution™ Work Space 458.

In some embodiments, most or all of the controls discussed below in thepresent application are implemented within control system 400. In oneembodiment, most or all controls are implemented within Allen-Bradley™PLC 402. For example, PID control blocks can be implemented usingprovided Allen-Bradley™ PID blocks, or the blocks can be created fromprimitive mathematical operations using ladder logic. Control blockssuch as the table blocks and selector blocks of FIGS. 24 and 25 may beimplemented within Allen-Bradley™ PLC 402 using standard blocks. Localon-site computer 440 may be used to store and output values such as PIDset points and selector switch values from local computer 440 toregisters or control blocks within PLC 402. For example, the set pointsto heat exchanger, differential pressure, and feed rate control blocksmay reside within local computer 440 and be downloaded to PLC 402. Theset points may be obtained by local computer 440 from a local terminaland/or from World Wide Web 424 from devices 426, 428, and/or 430,protected by appropriate security. Local computer 440 can be used toprovide historical trending, operator interface, alarming, andreporting.

Referring now to FIG. 17, a process graphic 450, as displayed on ahuman-machine interface is displayed. Process graphic 450 may bedisplayed, for example, on an Intellution™ IFIX system. Process graphic450 can be updated in real time and can reside on a personal computer,for example. Process graphic 450 includes a manual switch 458 and anautomatic switch 459 for controlling the control mode of thedifferential pressure across the bag house. Process graphic 450 alsoincludes a table of values 460 including the differential pressure setpoint, the actual differential pressure and the inlet temperature to thebag house. An output table 462 is also illustrated, including the baghouse outlet temperature, the flue gas flow rate, the inlet pressure tothe bag house and the outlet pressure from the bag house. A bag house452 is shown diagrammatically including an inlet 454 and an outlet 456.An outlet emission table 464 is also illustrated, including the SO₂, theNO_(X) level, and the O₂ level. Process graphic 450 may be used tomonitor and control the bag house differential pressure, as previouslydiscussed.

Referring now to FIG. 18, a process graphic 470 is illustrated as may bedisplayed on an Intellution™ IFIX process graphic. Process graphic 470can monitor and control the absorbent feeder speed, including anincrease button 471 and a decrease button 472. The actual feeder speedin pounds of sorbent per hour is illustrated at feeder speed 483. Ascrubber inlet table 473 is illustrated, including a SO₂ level, a NOlevel, a NO₂ level, a NO_(X) level, a CO level, and an O₂ level. Ascrubber outlet table 474 includes the same levels as the inlet, but atthe scrubber outlet. A NO_(X) control section 475 on the process graphicincludes a manual button 476 and an auto button 477, as well as a setpoint 478. In automatic mode, set point 478 may be used to control thefeeder speed using the NO_(X) set point. Similarly, an 502 controlsection 479 includes a manual control button 480 and an auto controlbutton 481, as well as a set point 482. In automatic mode, set point 479may be used to control the feeder speed using the SO₂ set point.

Referring now to FIG. 19, a process graphic 490 is illustrated, as maybe found on a process control and monitoring station. A cooler 491 isillustrated, having an inlet 492 and an outlet 493, with the inlet andoutlet temperatures being displayed in real time. Cooler 491 may be aheat exchanger as previously discussed. Process graphic 490 includes amanual button 494 and an auto button 495. The bag house inlettemperature is displayed at 498 as is the cooler set point 497. When inthe automatic mode, the fan speed may be controlled by a PID controllerusing set point 497. Process graphic 490 also includes an outletemission table 496, including the SO₂ level, the NO_(X) level, and theO₂ level.

Referring now to FIG. 20, differential pressure control loop 300 isillustrated in block diagram form. Differential pressure controller 302may be seen to accept set point 312 and actual differential pressure310, and to generate output signal 314 to control the differentialpressure across bag house 30. As previously discussed, differentialpressure set point 312 may be set taking into account the desiredpollutant removal target of the system, the power required to force gasthrough the filters, and the desired rate of sorbent replenishment.

Referring now to FIG. 21, sorbent feeder control loop 320 is illustratedin block diagram form. As previously discussed, feeder control loop 320can include a reaction zone CEM unit 80B that generates an output signalfrom the NO_(X) and/or SO_(X) emission analyzers. Emissions/Feedercontroller 322 can accept the NO_(X) or SO_(X) measured emission levelthrough controller input 328, and accepts a set point 326 indicating thedesired NO_(X) and/or SO_(X) concentration. Controller 322 may also senda controller output 332 to sorbent feeder 20. As previously discussed,sorbent feeder 20 may be a variable speed screw feeder, accepting avariable analog drive signal among others as its input from feedercontroller 322. The process trade-offs in setting set point 326 are aspreviously described.

FIG. 22 illustrates a control loop 341 for controlling the temperatureof bag house 82. Temperature controller 340 is as previously describedwith respect to FIG. 15. Temperature controller 340 accepts a bag housetemperature input 342 and desired bag house input temperature set point344, generating controller output 346 which can be fed as a fan speedcontrol to heat exchanger 72A. The control scheme rationale is aspreviously described with respect to FIG. 15.

Referring now to FIG. 23, a variable venturi control loop 361 isillustrated. FIG. 23 illustrates a venturi position controller 360,which accepts a venturi position set point 362 and an actual venturiposition input 364, generating a controller output 366 which can beaccepted by a variable venturi positioner at 368. The actual position ofthe variable venturi position may be measured by a position detector367. In one embodiment, the variable venturi position may be measured inunits of 0 to 100%. Venturi set point 362 may be set as a function ofone of several desired process parameters.

The variable venturi position may be set to control the space betweenthe variable venturi 160 and interior surface 154, the cross-sectionalflow area, available for the bag house inlet gas to flow around the flowoccluding devise, variable venturi 160, thereby controlling thefluidization velocity of the gas. When the flow cross-sectional area isdecreased, the gas flow velocity increases, which can be used to supporta deeper fluidized bed depth of sorbent material. If the gas flowvelocity is made very high, only the densest sorbent particles will beable to descend against the swiftly rising gas and be collected from thesystem. If the fluid velocity is set very low, even the lightestparticles will be able to settle out of the system quickly, therebyincreasing the need for regeneration or recycling of material back tothe reaction zone for more loading. A higher gas flow velocity will, ineffect, create a fluidized bed reactor, having a fluidized bed ofsorbent material held in place by the upwardly rising gas stream. Arapidly moving gas stream will also carry more sorbent particles to thefabric bags 88 filter to form a filter cake. Conversely, a slowly movinggas flow around the variable venturi 160 will allow many sorbentparticles to fall and be collected prior to becoming caked upon the bags88. A deeper fluidized bed will create higher differential pressures anda shallow fluidized bed will create lower differential pressures.Removal efficiencies may be taken into consideration when setting SO_(X)and/or NO_(X) fluidized bed depth. Variable venturi controller 360 maybe any suitable controller, including a PID controller, utilizing anycombination of its modes.

Referring now to FIG. 24, a control scheme 370 is illustrated forcontrolling sorbent feeder 20 using one set of inputs selected from thegroup including NO_(X) concentration, SO_(X) concentration, and reactorzone differential pressure. The control of sorbent feeder 20 may beaccomplished by selecting one of the aforementioned control inputs,where the selection may be based on the greatest deviation from setpoint or error.

An error generator 373 may be seen to accept several actual measurementsignals 384, as well as several set points 385. The actual signals andset points may be used to generate corresponding errors, for example,using subtraction. Error generator 373 may be seen in this example tooutput a NO_(X) error 373A, a SO_(X) error 373B, and a differentialpressure error 373C. The outputs from error generator 373 may beaccepted by an error selector gate 374, with one of the input errorsselected and output as the error to a controller error input 382. Errorselector gate 374 may be operated manually to accept one of the severalinput errors in some embodiments. In other embodiments, error selectorgate 374 may automatically select the largest error or deviation, tocontrol based on the process variable or parameter most requiringattention. For example, sorbent feeder 20 may be controlled based uponthe NO_(X) concentration, the SO_(X) concentration, or the differentialpressure across the reaction zone.

Error selector gate 374 may select the highest deviation, or the highestpercent of deviation, of these three error inputs. Error selector gate374 can generate a selector output 386 which can be used to select whichof the inputs a gain selector 372 is to select. Similarly, errorselector gate 374 may output a selector output 383 which can be acceptedby a set point selector gate 376 to select from various set pointsprovided to the selector gate.

A gain table 371 may be implemented as a table in a fixed database, forexample, a series of registers in a PLC. Gain table 371 may be seen toinclude a NO_(X) gain 371A, a SO_(X) gain 371B, and a differentialpressure gain 371C. The gains from gain table 371 may be seen to feedgain selector block 372. A gain selector output 377 may be sent to acontroller gain input 379.

A set point table 375 may be seen to include a NO_(X) set point 375A, aSO_(X) set point 375B, and a differential pressure set point 375C. Theset points may be used as inputs to selector gate 376, with selectoroutput 383 being used to select one of the input set points. Selectorgate 376 may be seen to output one of the selected set points tocontroller set point input 380.

Control scheme 370 thus provides a system and method for controlling thesorbent feeder rate based upon any one of the NO_(X) concentrations, theSO_(X) concentration or the differential pressure across the reactionzone. This can be accomplished using the selector blocks previouslydiscussed while only requiring a single controller. Controller 378 canbe, for example, a PID controller, using any combination of itsindividual modes.

Referring now to FIG. 25, a control scheme 390 is illustrated, similarin some respects to control scheme 370 of FIG. 24. Control scheme 390includes similar control blocks, tables, and outputs as previouslydescribed in FIG. 24. Control scheme 390 further includes the variableventuri control as one of the possible sets of inputs, gains, and setpoints to be used to control sorbent feeder 20. Gain table 371 may beseen to include a variable venturi gain 371D. Error generator 373 may beseen to generate a variable venturi error 373D. Set point table 375 maybe seen to include a variable venturi set point 375D. Control scheme 390may thus operate in a manner similar to control scheme 370 of FIG. 24,but allowing for control based on the venturi position.

Various components of the system of the invention have been discussedabove. Many of the components of the system are commercially availablefrom various original equipment manufacturers and are known to those ofordinary skill in the art. Further, one skilled in the art willrecognize and understand that the reaction zones and other units of thesystem of the invention may be connected by pipes, ducts, and lines,etc. which allow gas and/or sorbent to flow through and within thesystem and that reaction zones are in flow through communication in dualand multi stage embodiments of the invention. In addition to theaforementioned system components, the system may further include varioushoppers, conveyors, separators, recirculation equipment, horizontal andvertical conveyors, eductors. Further, there may be modulating divertervalves, vibrators associated with feeders, compressors to provideinstrument air to pulse filter fabric bags, as well as various metersand sampling ports.

In addition to removing SO_(X) and NO_(X), the system and processes ofthe invention can be utilized to remove mercury (Hg) and fly ash. Gasesemanating from combustion of fuels, which contain mercury and sulfides,include mercury compounds, mercury vapor, ash, SO_(X) and NO_(X). Thesegases and solids are commingled with oxides of manganese and aretransported at a sufficient velocity as a gas-solids mixture to areactor, which may be a bag house or other reactor/separating device.During transport and during residence in the reactor,oxidation-reduction reactions occur. These reactions cause theconversion of mercury vapor to mercury compound(s), and sorbent and/oralumina adsorb the mercury compound(s). As disclosed above, SO_(X) andNO_(X) are removed through reaction with oxides of manganese to formsulfate and nitrate compounds of manganese. These reaction products,unreacted sorbent (if any) alumina, adsorbed mercury, and ash aretrapped and collected in the bag house and clean, substantially strippedgases are vented to the stack. Thus, during the processing of gases withthe system of the invention, mercury and mercury compounds may also beremoved. The reacted and unreacted sorbent when removed from thereaction zones of the system may be further processed to generate usefulproducts and to regenerate the sorbent as described herein below.

The system of the invention in its various embodiments may be utilizedin a process for removal of oxides of sulfur and/or oxides of nitrogen,mercury (compounds and vapor), and other pollutants from a gas stream.The processes generally involve providing a system according to theinvention, whether single stage, dual-stage, or multi-stage. Gas andsorbent are introduced into a reaction zone and contacted for a timesufficient to effect capture of the targeted pollutant(s) therebysubstantially stripping the gas of the targeted pollutant(s). In asingle-stage removal process, the reaction zone would need to be asolid-gas separator operating as a reaction zone or else followed by asolid-gas separator in order to render the gas that has beensubstantially stripped of a target pollutant free of solids so that thegas may either be vented or directed for further processing. In adual-stage removal process, the second reaction would preferably be asolid-gas separator operating as a reaction zone. And, in a multi-stageremoval process the last reaction zone in the series of reaction zonesthrough which the process gas is directed would need to be a solid-gasseparator operating as a reaction zone or else followed by a solid-gasseparator in order to render the gas that has been substantiallystripped of a target pollutant free of solids so that the gas may eitherbe vented or directed for further processing. Generally, configuring thesystems and processes of the invention to incorporate a solid-gasseparator as the last reaction zone in a sequence of removal steps wouldbe most economical and efficient.

A process according to the invention is described below usingsingle-stage and dual-stage systems of the invention for purposes ofillustration. It should be readily understood by those skilled in theart that the processes as described can be adapted to multi-stageremovals and to removal of various targeted pollutants with or withoutthe addition of other sorbent materials or chemical additives, asappropriate.

Removal of SO_(X) and/or NO_(X) can be accomplished in a singlesingle-stage removal system. Sorbent and gas containing SO_(X) and/orNO_(X) are introduced into a reaction zone 30 where the gas and sorbentare contacted for a time sufficient to substantially strip the gas ofSO_(X) and/or NO_(X). If SO_(X) is the primary target pollutant, the gasmay be introduced at temperatures typically ranging from about ambienttemperature to below the thermal decomposition temperature(s) ofsulfates of manganese. If NO_(X) is the primary target pollutant, thegas would be introduced at temperatures typically ranging from aboutambient temperature to below the thermal decomposition temperature(s) ofnitrates of manganese. If both pollutants are present, NO_(X) will notbe captured if the temperature of the gas is above the thermaldecomposition temperature of nitrates of manganese. In the reactionzone, the gas would be contacted with the sorbent for a time sufficientto effect capture of the pollutant at a targeted capture rate. If bothpollutants are to be captured, the capture rate for the primary targetedpollutant would control or utilize a control sub-element, such ascontrol loop 320 of FIG. 14 or control loop 390 of FIG. 25. The capturerate for the targeted pollutants can be monitored and adjusted. Thereaction zone would preferably be a solid-gas separator that renders thegas free of solids, such as reacted and unreacted sorbent and any otherparticulate matter in the gas so that the gas may be vented from thereaction zone or directed for further processing, after contacting thegas with sorbent for a sufficient time.

In a dual-stage removal process, a system of the invention having atleast two reaction zones, first and second reaction zone 30, 38 as inFIG. 1, is provided. It should be understood that the system could be asystem of the invention such as the modular reaction units illustratedin FIGS. 2 and 3. With reference to FIG. 2, any of the bag houses 62,64, 66 could serve as first and second reaction zones 30, 38 dependingupon how the gas is directed through the system. Further, with referenceto FIG. 3, the first bag house 70 would correspond to first reactionzone 30 and either or both of the second and third bag houses 76, 78would correspond to second reaction zone 38. Additionally, it isunderstood that other reaction zones may be substituted for the baghouses of FIGS. 2 and 3 and the process as described could be carriedout.

However, for purposes of illustration, the dual-stage removal process isdiscussed with reference to FIG. 1. In this process of the invention,gas and sorbent are introduced into first reaction zone 30. The gas iscontacted with the sorbent for sufficient time to primarily effectSO_(X) capture at a targeted capture rate. The gas is rendered free ofsolids and then vented from the first reaction zone 30. Sorbent and thegas that has been substantially stripped of SO_(X) are then introducedinto second reaction zone 38. In the second reaction zone, the gas iscontacted with the sorbent for a sufficient time to primarily effectNO_(X) capture at a targeted capture rate. The gas is rendered free ofsolids and then vented from the second reaction zone 38. The vented gasmay be directed to stack 40 to be vented or emitted into the atmosphereor directed on for further processing.

With the processes of the invention, other pollutants that can becaptured with oxides of manganese can be removed. For example, withoutbeing limited or bound by theory, Applicants believe that mercurycompounds adsorb onto oxides of manganese. Applicants further believethat, in the system and processes of the invention, elemental mercury isoxidized to form oxides of mercury which also adsorb onto oxides ofmanganese. Additionally, hydrogen sulfide (H₂S) and other totallyreduced sulfides (TRS) can be removed utilizing oxides of manganese.More specifically, Applicants postulate that the sulfur in TRS may beoxidized to form SO₂ which is known to react with oxides of manganese toform sulfates of manganeseIt is known that mercury compounds may beremoved from gases by adsorption on fly ash and/or alumina. Thus,alumina may be introduced with the sorbent in a reaction zone forpurposes of removing mercury compounds and elemental mercury that has beoxidized to form oxides of mercury. Thus, elemental mercury that is notoxidized and therefore not captured by the sorbent in a first or secondreaction zone may be captured in a third reaction zone, which may bereferred to as a mercury-alumina reactor or an alumina reactor. Withrespect to single-stage removal, the mercury compounds may be removed ina reaction zone by contacting the gas with sorbent for a time sufficientfor the mercury compounds to adsorb on to the sorbent, and alumina ifmixed with the sorbent to thereby substantially strip the gas ofmercury. Further, if the reaction zone is a solid-gas separator, mercurycompounds adsorbed to fly ash would also be removed, therebysubstantially striping the gas of mercury compounds. In a dual-stage,the mercury compounds would similarly be removed, but depending uponwhich reaction zone is also a solid gas separator.

Thus, the system and process of the invention are readily understood toinclude and contemplate the removal of not only SO_(X) and/or NO_(X) butother pollutants, mercury compounds, elemental mercury, TRS, and H₂S.

The system and process of the invention has been tested at several powerplants utilizing a SO_(X) and/or NO_(X) removal demonstration unitembodying a system according to the invention. The demonstration unitutilized a bag house as the second reaction zone and a pipe/duct as afirst reaction zone in a dual stage removal system. The test runs andresults are summarized in the following examples.

EXAMPLE 1

NO_(X) concentrations were determined using EPA method 7E,chemiluminesent analysis method, and analyzed with a model 42Hchemiluminescent instrument manufactured by Thermo Electron Inc. Sulfurdioxide (SO₂) concentrations were measured utilizing, aspectrophotometric analysis method employing a Bovar Western ResearchSpectrophotometric model 921NMP instrument. In order to obtain accurateand reliable emission concentrations, sampling and reporting wasconducted in accordance with US EPA Reference CFR 40, Part 60, AppendixA, Method 6C. Gas flow rates in standard cubic feet per minute (scfm)were measured using AGA method #3, utilizing a standard orifice platemeter run. The demonstration was conducted utilizing a series of testruns on live gas streams from a power plant. Said power plant operatessteam boilers which are fired on high sulfur coal. During test runs,NO_(X) and SO₂ concentration readings were taken continuouslyalternating from the inlet and the outlet of the demonstration unit. Gasflow rates were measured continuously. The demonstration tests wereperformed utilizing two different forms of sorbent. The tests conductedutilized various forms of oxides of manganese as sorbent. The tests wereperformed with and without bag house filter pulsing. The following tablesummarizes the results and operational parameters:

Range of Operation Parameters Range of NO_(x) Concentrations Processed14.14 to 320 ppm by the Demonstration Unit Range of SO₂ ConcentrationsProcessed 300 to 1800 ppm by the Demonstration Unit Range of Gas Flowthrough the Demonstration 250 to 2000 scfm Unit Range of Pressure Acrossthe Bag House 0.5″ to 10.0″ of H₂O Range of Bag House Temperatures 60°F. to 246° F. Maximum NO_(x) steady state Removal Rate 96.0% Maximum SO₂steady state Removal Rate 99.8%

EXAMPLE 2

A test using the demonstration unit according to the invention,utilizing oxides of manganese as the sorbent was conducted on asimulated gas stream containing varying levels of NO_(X). Oxides ofmanganese powders that were used during this test described generally by60% of particles less than 45 microns in size and having a BET surfacearea of approximately 30 m²/g. Knowing that there is a competition forreaction sites between SO₂ and NO_(X), a series of tests was conductedto gather data on the efficiency of NO_(X) capture in the absence ofSO₂. Synthetic NO_(X) gas was made on site by use of high-concentrationbottle gas which was diluted into the inlet gas stream and processed bythe demonstration unit. The bag house was pre-loaded with oxides ofmanganese prior to introduction of test gas by operating thedemonstration unit's blower at high speed (typically about 1200 scfm),and feeding the oxides of manganese into the gas stream at a high rate(between 40% and 90% of feeder capacity) in order to form a suitablefilter cake on the fabric bags in the bag house. Gas from cylinderscontaining NO_(X), 20% NO, and 20% NO₂, (20,000 ppm) was metered intothe bag house inlet through a rotameter-type flow gage. NO_(X)concentrations were measured at the bag house inlet and outlet on analternating basis throughout the testing with the demonstration unit'scontinuous emissions monitoring system (CEMS), utilizing a ThermoElectron model 42H Chemiluminescent instrument. In order to obtainaccurate and reliable emission concentrations, sampling and reportingwas conducted in accordance with US EPA Reference CFR 40, Part 60,Appendix A, Method 6C.

Tests were performed at varying levels of bag house differentialpressure (measured in inches of water column) and flow rates (measuredin scfm). The NO_(X) inlet concentrations ranged from 18.3-376.5 ppmwith flow rates ranging from 260-1000. It has been determined thatvarying levels of filter cake thickness affect the NO_(X) and SO₂removal. A thicker filter cake increases the quantity of sorbent exposedto the gas, thus increasing the micro-reaction zone within the filtercake. As a representation of the sorbent filter cake depth, thedifferential pressure across the bag house (referred to as ΔP) wasmeasured between 2.00″-9.67″ of WC (expressed in inches of watercolumn). NO_(X) concentrations were recorded once the system was insteady state and the readings were stable for up to 20 minutes. Thefollowing table illustrates the level of NO_(X) removal achieved as afunction of inlet concentration, gas flow rate, and bag housedifferential pressure:

Summary of Bottle Gas NO_(x) Reduction Test Inlet Outlet Flow Run NO_(x)NO_(x) % ΔP Rate No. (ppm) (ppm) Reduction (in. H₂O) (scfm) 1 25.5 3.387.1 2.00 260 2 140.1 8.5 94.0 3.86 500 3 102.0 10.5 89.7 7.71 1000 4324.9 17.4 94.7 7.78 1000 5 195.0 15.1 92.3 7.85 1000 6 46.7 8.4 81.97.85 1000 7 200.3 32.5 83.8 3.0 to 4.0 1000 8 28.2 6.2 78.0 7.80 500 957.8 11.4 80.3 2.10 500 10 84.9 8.9 89.5 3.80 500 11 86.0 8.9 89.7 3.80500 12 194.5 11.5 94.1 3.80 500 13 317.5 12.7 96.0 3.80 500 14 376.526.7 92.9 2.10 500 15 376.5 26.7 92.9 2.10 500 16 18.3 4.0 78.1 4.45 50917 83.5 8.7 89.6 4.45 509 18 40.1 5.9 85.3 4.45 509 19 83.5 8.7 89.64.45 509 20 21.5 4.5 79.2 4.74 500 21 45.7 6.5 85.8 4.75 500 22 92.1 8.690.7 4.75 500 23 201.1 11.5 94.3 4.76 500 24 317.5 14.0 95.6 4.79 500 2552.1 10.0 80.9 9.67 1000 26 82.4 12.0 85.5 9.67 1000 27 105.4 13.2 87.59.65 1000 28 224.0 18.5 91.8 9.67 1000 29 328.4 23.1 93.0 9.67 1000 30100.2 15.0 85.0 9.67 1000

EXAMPLE 3

A further test of the demonstration unit according to the inventionutilizing oxides of manganese as the sorbent, was conducted on a liveexhaust gas slipstream from a 170 MW coal fired boiler. The boiler wasoperating on high sulfur coal of approximately 4-6% sulfur, resulting inmission concentrations of SO₂ in the range of 1200-2000 ppm and NO_(X)concentrations in the range of 280-320 ppm. A slipstream averaging 1000scfm was diverted from the main stack exhaust and routed to thedemonstration unit for reaction and sorption by the sorbent oxides ofmanganese. SO₂ and NO_(X) concentrations were measured at the scrubberinlet and outlet of the bag house on an alternating basis throughout thetesting with the demonstration unit's continuous emissions monitoringsystem (CEMS). SO₂ concentrations were measured utilizing a BovarWestern Research model 921NMP spectrophotometric analyzer and NO_(X)concentrations were measured utilizing a Thermo Electron model 42Hchemiluminescent instrument. In order to obtain accurate and reliableemission concentrations, sampling and reporting was conducted inaccordance with US EPA Reference CFR 40, Part 60, Appendix A, Method 6C.

SO₂ removal efficiencies of 99.8% and NO_(X) removal efficiencies of75.3% were achieved while processing on average 1000 scfm of exhaust gasat temperatures typically ranging from 150° F. to 250° F. Test runs wereconducted with varying levels of bag house differential pressuresranging from 0.5″ to 8.6″ of WC, which represents various levels offilter cake thickness. Tests were also conducted with different rates ofbag house filter bag pulsing and varying levels of oxides of manganesefeed rates. Oxides of manganese powders that were used during this testdescribed generally by 60% of particles less than 45 microns in size andhaving a BET surface area of approximately 30 m²/g. The following tablegives an example of SO₂ and NO_(X) data collected during a test in which1000 scfm was processed by the dry scrubber at an inlet temperature of250° F., and a differential pressure of 5.75″ of WC. Data was collectedonce the demonstration unit was in a steady state of NO_(X) and SO₂removal for a period of 30 minutes. The results are summarized in thebelow table:

Pollutant Inlet ppm Outlet ppm ppm % Removal Oxides of Nitrogen (NO_(x))285.9 70.5 75.3% Sulfur Dioxide (SO₂) 11703  3.9 99.8%

EXAMPLE 4

An additional series of demonstration tests of the demonstration unit,utilizing oxides of manganese as the sorbent, was conducted on a liveexhaust gas slipstream from a 75 MW coal fired boiler. This boiler wasoperating on Powder River Basin (PRB) coal, resulting in emissionconcentrations of SO₂ in the range of 340-500 ppm with NO_(X)concentrations in the range of 250-330 ppm. A slipstream ranging from500-1000 scfm was diverted from the main stack exhaust and routed to thedemonstration unit for reaction and sorption by the oxides of manganese.Oxides of manganese powder that were used during this test describedgenerally by 60% of particles less than 45 microns in size and having aBET surface area of approximately 30 m²/g. SO₂ and NO_(X) concentrationswere measured at the bag house inlet and outlet on an alternating basisthroughout the test with the demonstration unit's continuous emissionsmonitoring system (CEMS). SO₂ concentrations were measured utilizing aBovar Western Research model 921NMP spectrophotometric instrument andNO_(X) concentrations were measured utilizing a Thermo Electron model42H chemiluminescent instrument. In order to obtain accurate andreliable emission concentrations, sampling and reporting was conductedin accordance with US EPA Reference CFR 40, Part 60, Appendix A, Method6C.

SO₂ and NO_(X) reduction efficiencies were measured at 99.9% and 91.6%respectively. Testing was conducted with varying degrees of differentialpressure (ΔP) across the bag house to affect the residence time of thetargeted pollutants. Reaction chamber temperatures ranged from 150° F.to 280° F. It was determined that longer residence times resulted inimproved capture rates for NO_(X). However, the fact that the SO₂reaction occurs so rapidly and completely, the SO₂ reduction efficiencyremains nearly complete (99.9%) at even the lowest of residence times.While operating the scrubber at 0.5″-1.0″ of WC across the bag house, apollutant concentration reduction efficiency of 99.8% for SO₂ and 40.0%for NO_(X) was achieved. It is from these results that the concept for atwo stage reaction chamber system develops, whereby the first reactionchamber captures the majority of SO₂ and a small fraction of NO_(X),while the second “polishing” stage completes the NO_(X) removal todesired levels of efficiency, predetermined and controlled by the systemoperator. Data was collected once the dry scrubber was in a steady stateof NO_(X) and SO₂ removal for a period of 30 minutes. The followingtable gives an example of SO₂ and NO_(X) data collected during a testingin which 500 scfm was processed by the demonstration unit at an inlettemperature of 250° F., and a differential pressure of 8.7″ of WC:

Pollutant Inlet ppm Outlet ppm ppm % Removal Oxides of Nitrogen (NO_(x))268.1 22.4 91.6% Sulfur Dioxide (SO₂) 434.3  0.5 99.9%

EXAMPLE 5

In an attempt to determine the effectiveness of SO₂ and NO_(X) removal,a series of lab-scale tests were conducted utilizing a glass reactor.The reactor was designed to mimic the gas-solid interactions known to bepresent in the aforementioned demonstration unit. The glass reactor hada diameter of 2 inches with a length of approximately 24 inches. 50.0grams of oxides of manganese were suspended in the reactor using afritted glass filter allowing for flow of the gas stream, while keepingthe oxides of manganese suspended. Approximately 3 inches above thefluidized bed of oxides of manganese, a sintered stainless steel filterwas arranged to simulate a bag house filter bag. The reactor was heatedduring the testing to 250° F. and the gas flow rate was metered at aconstant 6 liters per minute (lpm). Simulated exhaust gas was producedby use of a calibration gas standard having the following composition:CO₂=17.35%, NO_(X)=391 ppm, SO₂=407 ppm, CO=395 ppm, and balance N₂. Thesimulated flue gas stream passed through the fluidized bed of oxides ofmanganese, where the flow carried a portion of the sorbent up onto thefilter, thus creating a filter cake, which mimics a bag house reactorchamber.

SO₂ and NO_(X) concentrations were measured continuously from thereactor outlet utilizing a continuous emissions monitoring system(CEMS). SO₂ concentrations were measured utilizing a Bovar WesternResearch model 921NMP spectrophotometric instrument and NO_(X)concentrations were measured utilizing a Thermo Electron model 42Hchemiluminescent instrument. In order to obtain accurate and reliableemission concentrations, sampling and reporting was conducted inaccordance with US EPA Reference CFR 40, Part 60, Appendix A, Method 6C.Removal efficiencies of 99.9% for SO₂ as well as 99.9% for NO_(X) weremeasured and duplicated for several test runs. Inlet temperature was250° F., with a differential pressure of 2.00″ of WC. The followingtable gives an example of SO₂ and NO_(X) data collected during testingin which 6 lpm of gas was processed by a glass reactor:

Inlet Outlet Sorbent % Flow rate ΔP Temp. Time with >94% Pollutant (ppm)(ppm) Weight (g) Removal (lpm) (in H₂O) (° F.) Removal Oxides ofManganese Type A NO_(x) 391 17.21 50 95.6% 6 2.00 250 29 min SO₂ 407 0.150 99.9% 6 2.00 250 >54 min   Oxides of Manganese Type B NO_(x) 391 0.150 99.9% 6 2.00 250 60 min SO₂ 407 0.1 50 99.9% 6 2.00 250 >90 Oxides onManganese Type C NO_(x) 391 0.2 50 99.9% 6 2.00 250 34 min SO₂ 407 0.150 99.9% 6 2.00 250 >68 min  

The tests of this Example 5 were conducted with three different lots ofmanganese oxide sorbent. FIGS. 29 and 30 are, respectively, graphsplotting NO_(X) and SO_(X) concentrations at the outlet of the glassreactor versus time. The three different oxides of manganese arerepresented by the symbols “⋄” for type A sorbent, “Δ” for type Bsorbent, and “□” for type C sorbent in FIGS. 29 and 30. Type A sorbentis an oxide of manganese powder generally at 60% of particles less than45 microns in size and having a BET surface area of approximately 30m²/g. Type B sorbent is an oxide of manganese powder generally at 100%of particles less than 45 microns in size and having a BET surface areaof approximately 200 m²/g. Type C sorbent is an oxide of manganesepowder generally at 80% of particles less than 45 microns in size andhaving a BET surface area of approximately 90 m²/g. The graph of FIG.30, confirms the above statements regarding near immediate and completeSO_(X) capture upon contact with the sorbent. The graph of FIG. 29 showsa range of capture efficiency over time for NO_(X) and that differentforms of oxide manganese may be able to provide more efficient captureof NO_(X). The type B sorbent performed the best before break-through,followed by type C. Useful captures were observed for all three types.With the process controls of the invention a wide variety of oxides ofmanganese can be utilized to effect removal at targeted capture rates.Further, the graphs of FIGS. 29 and 30 show that high removal or capturerates can be achieved and sustained over time. The operationalparameters of the systems of the invention can be monitored and adjustedto attain and maintain removal or capture rates at these high levels.

As mentioned above, the reacted or loaded sorbent can be recycled and/orregenerated after being removed from a reaction zone. For recyclingpurposes the reacted sorbent may simply be reintroduced into anotherreaction zone. For example with reference to FIG. 4, the system hasfirst and second reaction zones 30, 38 which are connected to feeder 20which contains unreacted or virgin sorbent. Gas from external gas source15 is introduced into first reaction zone 30 along with sorbent fed fromfeeder 20. The gas is contacted with sorbent for a time sufficient toremove a target pollutant, such as SO_(X), and after being rendered freeof solids is vented from the first reaction zone 30. The gas is thenintroduced in the second reaction zone 38 along with sorbent from feeder20. In the second reaction zone 38, the gas is contacted with gas for atime sufficient to remove another target pollutant, here NO_(X). Duringoperation, the level of NO_(X) loading on the reacted sorbent in secondreaction zone 38 reaches the point where the sorbent no longerefficiently removes NO_(X). When the point is reached, the NO_(X).reacted sorbent is removed from the second reaction zone 38 and conveyedor transported to NO_(X) reacted sorbent feeder 21. The NO_(X) reactedsorbent, which has unused reactive sites available for further SO_(X)capture, is fed or introduced into the first reaction zone 30 foradditional loading or reaction with SO_(X) in the gas introduced fromexternal gas source 15. When the recycled NO_(X) reacted sorbent reachesthe point where SO_(X) capture can no longer be achieved at a targetedrate of removal, the now NO_(X) and SO_(X) reacted (or loaded) sorbentis removed from the first reaction zone and routed for regeneration. Inthis way, the amount of virgin or unreacted sorbent that is utilized inthe first reaction zone can be reduced and the additional load orreactive sites available on the NO_(X) reacted sorbent can be utilized.

During a wet regeneration process the reacted surfaces of the sorbentmay be removed and the remaining sorbent may be refreshed. This will beunderstood with reference to FIG. 26. In a wet regeneration, reactedsorbent is removed from a reaction zone, a reaction chamber in FIG. 26,and washed in an aqueous dilute acid rinse. Since the interactionbetween pollutants and the sorbent is believed to be asurface-controlled phenomenon, only a small fraction of the oxides ofmanganese is reacted with the pollutant. It is this small fraction ofthe sorbent that can be removed by washing or rinsing which thereby“activates” the sorbent by making unreacted surface area available. Thesolubility in water of nitrates of manganese is greater than thesolubility of sulfates of manganese by at least an order of magnitude incold water and by at least several orders of magnitude in warm to hotwater. This differential in solubility can be advantageously utilized inthe regeneration process.

The sulfates and nitrates of manganese on the surface of the sorbentparticles dissolve off into solution in the dilute acid bath, leavingclean sorbent that can be readily separated from the rinse or bath byknown means, such as settling and decanting, filtering, centrifuging orother suitable techniques. As is further discussed below, the clearfiltrate or solution containing dissolved sulfates and/or nitrates ofmanganese are directed to a regeneration vessel for regeneration ofsorbent and production of useful by-products. The clean sorbent is thendried in, for example, a kiln to remove excess moisture. The heat forthis drying step may be waste heat generated by combustion which istransferred or exchanged from combustion or process gases at anindustrial or utility plant. After drying, the clean sorbent may bepulverized as necessary to reduce the clean sorbent to particle sizesuseful in the system of the invention. The cleaned or “activated”sorbent is then conveyed or otherwise transported to the unreactedsorbent feeder(s) and thus, recycled.

Again with reference to FIG. 26, the regeneration of sorbent andproduction of useful by-products can be understood. The solution orfiltrate containing the dissolved sulfates and nitrates of manganese ispassed from the acidic bath to a regeneration vessel to which alkalihydroxides such as potassium hydroxide (KOH) or sodium hydroxide (NaOH),or ammonium hydroxide (NH₄OH) is added. The addition of thesehydroxides, yield respectively, a solution containing nitrates and/orsulfates of potassium, sodium, or ammonium. These solutions can be madeinto fertilizer products or other products such as explosives. Air oroxygen is bubbled into or otherwise introduced into the reaction vesselto complete the regeneration, forming oxides of manganese, MnO_(X) whereX is between about 1.5 to 2.0.

The oxides of manganese are separated from the solution, much as thecleaned or reactivated sorbent after the acid wash step, and are thendried and pulverized before being conveyed to a virgin or unreactedsorbent feeder. The filtrate from the separation containing usefulsulfates and nitrates that can then be further processed into marketableproducts.

Oxides of manganese may also be regenerated in a dry or thermalregeneration process, taking advantage of the thermal decompositiontemperature(s) of nitrates of manganese. This regeneration process maybe understood with reference to FIG. 27. The process illustrated anddiscussed herein is based upon a removal process where NO_(X) is thetarget pollutant with nitrates of manganese being formed in the removalstep in the reaction zone, a reaction chamber in FIG. 27. The NO_(X)reacted sorbent is removed from the reaction chamber and conveyed to afirst kiln. In the first kiln, the reacted sorbent is heated to atemperature at or above the thermal decomposition temperature(s) ofnitrates of manganese and NO₂ desorbs or is otherwise driven off. Oxidesof manganese, MnO_(X) where X ranges from about 1.5 to 2.0 are formed inthe first kiln which may be heated with waste process heat from thelocal plant. The regenerated oxides of manganese from the first kiln maybe conveyed to a second kiln heated with waste process heat. Air oroxygen are introduced into the second kiln to more completely oxidizethe regenerated sorbent so that the X of MnO_(X) ranges from about 1.5to 2.0.

If the sorbent was SO_(X)-reacted the thermal regeneration would proceedmuch as described for NO_(X), except the first kiln would be heated to atemperature at or above the thermal decomposition temperature ofsulfates of manganese and SO₂ would desorb or otherwise driven off. Without being bound by theory, Applicants believe that nitrates of manganesethermally decompose at temperatures between about 130° C. to about 260°C., while sulfates of manganese tend to liquefy at the temperatures overwhich nitrates of manganese thermally decompose. Applicants furtherbelieve that sulfates of manganese heated to these temperatures in thepresence of a reducing agent, e.g., CO, H₂, etc., will decompose to SO₂and MnO. Thus, if the sorbent were reacted with both SO_(X) and NO_(X),NO₂ could be driven off first by heating reacted sorbent in a kiln to afirst temperature at which nitrates of manganese thermally decompose sothat NO₂ can be generated and directed for further processing. Areducing agent could then be introduced and the reacted sorbent furtherheated to desorb SO₂. Alternatively, the reacted sorbent could be heatedto a second temperature, the thermal decomposition temperature ofsulfates of manganese with SO₂ being desorbed and directed for furtherprocessing. The desorbed SO₂ can be directed to a wet scrubbercontaining water and an optional oxidant to form sulfuric acid. Thisacid liquor can then be marketed as is or further processed. Thisfurther processing would involve the addition of an ammonium or alkalihydroxide solution to form useful sulfates. In either case, theregenerated sorbent is further heated in an oxidizing atmosphere to morecompletely oxidize the regenerated sorbent so that the X of MnO_(X)ranges from about 1.5 to 2.0.

Referring back to FIG. 27, the desorbed NO₂ can be directed to a wetscrubber containing water and an oxidant to form nitric acid. This acidliquor can then be marketed as is or further processed. This furtherprocessing would involve the addition of an ammonium or alkali hydroxidesolution to form useful nitrates, such as KOH as illustrated in FIG. 27.

In addition to regeneration of sorbent and production of usefulby-products from the sulfates and nitrates of manganese, elementalmercury can be recovered for NO_(X), SO_(X) reacted sorbent that furtherhas mercury compounds adsorbed thereon can be processed to generate andrecover elemental mercury. The reacted sorbent is removed from areaction zone of a system according to the invention and conveyed to afirst kiln, the reacted sorbent is heated to a first temperature todesorb NO₂ which is routed for further processing into marketableproducts. The reacted sorbent is then heated a second temperature todesorb elemental mercury which is routed to a condenser for recovery asa marketable product. The sorbent is then rinsed to wash away any ashand to dissolve sulfates of manganese into solution to form a liquor.Any ash in the liquor is separated out and the ash routed for furtherhandling. Alkali or ammonium hydroxide is added to the liquor to form anunreacted sorbent precipitate of oxides of manganese and a liquorcontaining alkali or ammonium sulfates. The liquor contains rinsedsorbent. The rinsed sorbent and unreacted sorbent precipitate and areseparated from the liquor and the liquor is routed for furtherprocessing into marketable products or for distribution and/or sale as auseful by-product. The rinsed sorbent and sorbent precipitate are driedto form unreacted sorbent which can then be pulverized to de-agglomeratethe unreacted sorbent.

Liquid mercury can also be recovered from mercury adsorbed to alumina inan alumina reactor. The mercury-reacted alumina from the reactor isheated to drive off or desorb mercury. The mercury vapor is thendirected to a condenser where it is condensed to form liquid mercurywhich is a marketable product.

The above examples of regeneration processes are provided by way ofexample and are not intended to limit the processes, both known andunknown, for regeneration of oxides of manganese and for recovery ofuseful and marketable by-products that may be incorporated into theprocesses of the invention.

The combustion of fossil fuels (e.g., coal, oil, and natural gas)liberates three major air pollutants: (1) particulates (2) sulfurdioxide (SO₂) and (3) oxides of nitrogen (NO_(X)). Wet scrubbing,electrostatic precipitators and bag houses can remove particulates suchas fly ash. Using mechanical filters or electrostatic precipitators doesnot remove SO₂, SO₃, NO₂, N₂O₄, NO, or N₂O₃. Prior technologies haveused wet scrubbing for the process as a means of sorbing SO_(X) andNO_(X). Water is effective as a scrubbing medium for the removal of SO₂;removal efficiencies can be improved by the addition of chemicalabsorbents such as calcium, magnesium and sodium. However, nitrogenoxide (NO) is essentially insoluble in water, even with the use ofsorbtion chemicals. Residence times required and liquid-to-gas surfaceareas have proven to be impractical where high gas flow rates areencountered such as boiler flue gas.

Some of the economics involved in the wet scrubbing process involvehigh-energy consumption; on the average 4-5% of a plant gross powergeneration is consumed in the process. For example: (1) highdifferential pressure of a venturi/absorber tower requires 30″ of WC ora bag house and scrubber combination requires even higher staticpressures. (2) Large volumes of high pressure scrubbing liquor injectedthrough nozzles into the scrubbing apparatus. (3) Slurry tanks requiringcontinual vigorous agitation. (4) High horsepower required to forcewater-saturated non-buoyant flue gas up the stack.

Environmental drawbacks of existing systems include large quantities ofminerals used as sorbents and the insoluble sulfites or sulfate formedfrom the scrubbing reaction. The precipitate is then taken to landfillsor holding ponds. Some other disadvantages of existing systems arefouling of the internal scrubber components with hard scale, increasingoperational labor and maintenance costs. Some complex regenerativesystems use large quantities of chemicals required to react with themillions of gallons of slurry used every day.

The dry scrubbing process described in this patent is effective inremoving nearly all NO_(X) and SO_(X). Differential pressurerequirements through the scrubber should typically not exceed 10 inchesof water column and residence times within the sorbent cake aretypically less than 1 second. Volumes of sorbent used in this inventionin comparison to the wet slurry volumes are miniscule and recharging ofreaction zones are done periodically. While stack gases remain dry andhot, some waste heat will be used in the drying of washed andre-generated sorbent. Operational costs of the reaction zone(s) aresimilar to operating an ash bag house; also capital expenditures areestimated to be reasonable requiring standard off-the-shelf equipmentand instrumentation.

As a summary, the equipment is used in the dry scrubbing process is muchless complex than the wet scrubber process thus requiring loweroperational maintenance costs and a reduced operating staff. Chemicaland raw material costs are expected to be similar with less wasteeffluent produced. The major cost savings will be in the reduced powerconsumption expected to be significantly less than that of a wetscrubbing system, with fan horsepower reduction making up the majorityof the savings.

While exemplary embodiments of this invention and methods of practicingthe same have been illustrated and described, it should be understoodthat various changes, adaptations, and modifications might be madetherein without departing from the spirit of the invention and the scopeof the appended claims.

1. A system for dry removal of target pollulants from a gas, comprising:A. at least one feeder containing a supply of sorbent of regenerableoxides of manganese and/or regenerated oxides of manganese; wherein theat least one feeder is configured to handle and feed oxides of manganesewhich, upon regeneration, are in particle form and are defined by thechemical formula MnO_(X), where X is about 1.5 to 2.0 and wherein theoxides of manganese have a particle size of less than about 0.1 to about500 microns and a BET value ranging from about 1 to about 1000 m²/g; B.a modular reaction unit comprised of at least three (3) interconnectedbag houses configure to receive gas and sorbent, the bag houses beingconnected so that a gas containing target pollutants, including at leasta first target pollutant and/or a second target pollutant, can be routedthrough any one of the bag houses, any two of the bag houses in series,or all of the at least three bag houses in series or in parallel, or anycombination of series and parallel, each bag house being separatelyconnected to the at least one feeder so that sorbent can be introducedinto each bag house where first and/or second target pollutant capturecan occur when the gas is contacted with sorbent for a time sufficientto allow formation a first and/or a second reaction product formed byreaction between the first and/or second target pollutant and the oxidesof manganese; and C. a controller for simultaneously monitoring andadjusting system operational parameters, the controller providingintegrated control of system differential pressure and other operationalparameters selected from the group consisting of first and/or secondpollutant capture rate, gas inlet temperature, sorbent feed rate and anycombination thereof, wherein differential pressure within the system isregulated so that any differential pressure across the system is nogreater than a predetermined level and the first and/or second pollutantare removed at targeted capture rates.
 2. A system for dry removal oftarget pollutants including at least oxides of sulfur (SO_(X)) and/oroxides of nitrogen (NO_(X)) from gases, comprising: A. At least onefeeder containing a supply of sorbent of regenerable oxides of manganeseand/or regenerated oxides of manganese; wherein the at least one feederis configured to handle and feed oxides of manganese which, uponregeneration, are in particle form and are defined by the chemicalformula MnO_(X), where X is about 1.5 to 2.0 and wherein the oxides ofmanganese have a particle size of less than about 0.1 to about 500microns and a BET value ranging from about 1 to about 1000 m²/g; B. Amodular reaction unit comprised of at least three (3) interconnected baghouses configure to receive gas and sorbent, the bag houses beingconnected so that a gas containing target pollutants including at leastSO_(X) and/or NO_(x) can be routed through any one of the bag houses,any two of the bag houses in series, or all of the at least three baghouses in series or in parallel, or any combination of series andparallel, each bag house being separately connected to the at least onefeeder so that sorbent can be introduced into each bag house whereSO_(X) and/or NO_(x) capture can occur when the gas is contacted withsorbent for a time sufficient to allow formation of sulfates ofmanganese, nitrates of manganese, or both; and C. a controller forsimultaneously monitoring and adjusting system operational parameters,the controller providing integrated control of system differentialpressure and other operational parameters selected from the groupconsisting of target pollutant capture rates, SO_(X) and/or NO_(x)capture rate, gas inlet temperature, sorbent feed rate and anycombination thereof, wherein differential pressure within the system isregulated so that any differential pressure across the system is nogreater than a predetermined level and the SO_(X) and/or NO_(x) areremoved at targeted capture rates.
 3. A system for dry removal of oxidesof sulfur (SO_(X)) and/or oxides of nitrogen (NO_(x)) from gases,comprising: A. At least one feeder containing a supply of sorbent ofregenerable oxides of manganese and/or regenerated oxides of manganese;wherein the at least one feeder is configured to handle and feed oxidesof manganese which, upon regeneration, are in particle form and aredefined by the chemical formula MnO_(X), where X is about 1.5 to 2.0 andwherein the oxides of manganese have a particle size of less than about0.1 to about 500 microns and a BET value ranging from about 1 to about1000 m²/g; B. A modular reaction unit comprised of at least three (3)interconnected bag houses configured to receive gas and sorbent, the baghouses being connected so that a gas containing target pollutantsincluding at least SO_(X) and/or NO_(X) can be rowed through any one ofthe bag houses, any two of the bag houses, or all of the at least threebag houses in series, in parallel, or any combination of series andparallel, each bag house being separately connected to the at least onefeeder so that sorbenr can be introduced into each bag house whereSO_(X) and/or NO_(X) capture can occur when the gas is contacted withsorbent for a time sufficient to allow formation of sulfates ofmanganese, nitrates of manganese, or both, with SO_(X) being captured byreacting with the sorbent to form sulfates of manganese to substantiallystrip the gas of SO_(X) and NObeing captured by reacting with thesorbent to form nitrates of manganese to substantially strip the gas ofNO_(X), the bag houses each being configured to render the gas that hasbeen substantially stripped of SO_(X) and/or NO_(X) free of reacted andunreacted sorbent so that the gas that has been substantially strippedof SO_(X) and/or NO_(X) may be vented from the bag houses or passed fromone bag house to another bag house in series; and C. a controller forsimultaneously monitoring and adjusting system operational parameters,the controller providing integrated control of system differentialpressure and other operational parameters selected from the groupconsisting of target pollutant capture rates, SO_(X) and/or NO_(X)capture rate, gas inlet temperature, sorbent feed rate and anycombination thereof, wherein differential pressure within the system isregulated so that any differential pressure across the system is nogreater than a predetermined level and the SO_(X) and/or NO_(X) areremoved at targeted capture rates.
 4. The system of any one of claims1-3, further comprising at least one reacted sorbent feeder, the reactcdsorbent feeder being configured to receive reacted sorbent from one baghouse of the system and to introduce reacted sorbent into the same baghouse or into another bag house of the system.
 5. The system of any oneof claims 1-3, further comprising a reacted sorbent regenerationsubsystem.
 6. The system of any one of claims 1-3, further comprising anaqueous sorbent treatment subsystem, wherein the sorbent is treated toimprove sorbent loading capacity and/or capture efficiency.
 7. Thesystem of any one of claims 1-3, further comprising an aqueous sorbenttreatment subsystem, wherein the sorbent is treated to activate thesorbent and improve sorbent loading capacity and/or capture efficiency.8. The system of any one of claims 1-3, further comprising an aqueoussorbent treatment subsystem, wherein the sorbent is regenerated forreuse.
 9. The system of any one of claims 1-3, further comprising anaqueous sorbent treatment subsystem, wherein the sorbent is regeneratedfor reuse and by-products are formed.
 10. The system of any one ofclaims 1-3, further comprising a thermal regeneration subsystem whereinsorbent is regenerated for reuse.
 11. The system of claim 2 or 3,wherein the targeted capture rates for both SO_(X) and NO_(X) are set nolower than 60%, SO_(X) is removed at a steady state removal rate of atleast 60%, and NO_(X) is removed at a steady state removal rate of atleast 60.0%.
 12. The system of claim 2 or 3, wherein the targetedcapture rates for both SO_(X) and NO_(X) are set no lower than 70.0%,SO_(X) is removed at a steady state removal rate of at least 70.0%, andNO_(X) is removed at a steady state removal rate of at least 70.0%. 13.The system of claim 2 or 3, wherein the targeted capture rates for bothSO_(X) and NO_(X) are set no lower than 80.0%, SO_(X) is removed at asteady stare removal rate of at least 80.0%, and NO_(X) is removed at asteady state removal rate of at least 80.0%.
 14. The system of claim 2or 3, wherein the targeted capture rates for both SO_(X) and NO_(X) areset no lower than 90.0%, SO_(X) is removed at a steady state removalrate of at least 90.0%, and NO_(X) is removed at a steady state removalrate of at least 90.0%.
 15. The system of claim 2 or 3, wherein thetargeted SO_(X) capture rate is at least 98.0%, SO_(X) is removed at asteady state removal rate of at least 98.0%, the targeted NO_(X) capturerate is at least 90.0% and NO_(X) is removed at a steady state removalrate of at least 90.0%.
 16. The system of claim 2 or 3, wherein thetargeted SO_(X) capture rate is at least 99.0%, SO_(X) is removed at asteady state removal rate of at least 99.0%, the targeted NO_(X) capturerate is at least 92.0% and NO_(X) is removed at a steady state removalrate of at least 92.0%.
 17. The system of claim 15, wherein the targetedNO_(X) capture rate is at least 94.0% and NO_(X) is removed at a steadystate removal rate of at least 94.0%.
 18. The system of claim 15,wherein the targeted NO_(X) capture rate is at least 95.0% and NO_(X) isremoved at a steady state removal rate of at least 95.0%.